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Veterinary Immunology and Immunopathology 145 (2012) 191– 198

Contents lists available at SciVerse ScienceDirect

Veterinary Immunology and Immunopathology

j ourna l ho me pag e: www.elsev ier .com/ locate /vet imm

esearch paper

istological, histochemical and immunohistochemical study of theymph nodes of the one humped camel (Camelus dromedarius)

ohamed Zidana, Reinhard Pabstb,∗

Department of Histology and Cytology, Faculty of Veterinary Medicine, Alexandria University, 22758 Edfina, Elbehera, EgyptInstitute of Immunomorphology, Center of Anatomy, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany

r t i c l e i n f o

rticle history:eceived 17 May 2011eceived in revised form 8 November 2011ccepted 9 November 2011

eywords:ymph nodeistochemistry

mmunohistologylectron microscopyamel

a b s t r a c t

Prescapular, femoral, mesenteric, mediastinal and splenic lymph nodes from nine camels ofone to 12 years of age were studied. There were no obvious structural differences betweenthese different lymph nodes or between the ages. The lymph nodes were surrounded by acapsule formed of two layers, an outer thicker layer of connective tissue and an inner thinnerlayer mainly of smooth muscles. Trabeculae extended from the inner layer of the capsuledividing the parenchyma characteristically into incomplete lobules. Subcapsular and tra-becular lymphatic sinuses were supported by a reticular fiber network. The parenchymawas uniquely different from that of other species, as it was arranged in the form of lym-phoid follicles and interfollicular lymphoid tissue. The lymphoid follicles of CD22 positivelymphocytes were supported by a reticular fiber network. This fine network of �-smoothmuscle actin positive cells enclosed the lymphoid follicles. The interfollicular tissue wasmainly made up of diffusely distributed CD3 positive lymphocytes. MHC class II: DR wasexpressed by most lymphocytes of the follicles and interfollicular tissue. Lymphatic sinusesand high endothelial venules were found in the interfollicular zone. The lymphatic sinuses

were lined by discontinuous endothelial cells. The wall of the high endothelial venules wasinfiltrated by several lymphocytes and enclosed in a layer of �-smooth muscle actin positivecells. Acid phosphatase positive cells were evenly distributed in the interfollicular zone. Afew cells were localized in the lymph follicles. Alkaline phosphatase was observed in theendothelium of the lymphatic sinuses and in the lymphoid follicles.

. Introduction

Lymph nodes are independent lymphatic organs lyinglong the course of lymphatic vessels. They play an essen-ial role in regional immunity (Dellman and Brown, 1981),nd have veterinary significance in meat inspection as

hey reflect the health of the region they drain (Wilson,991). Camels are an important source of meat, milk, woolnd hide in several countries and are used also in racesnd for transport in some countries. There is a growing

∗ Corresponding author. Tel.: +49 511 532 6742; fax: +49 511 532 8256.E-mail address: pabst.reinhard@mhhannover.de (R. Pabst).

165-2427/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.vetimm.2011.11.004

© 2011 Elsevier B.V. All rights reserved.

interest in camel meat and milk products. Previous pub-lications have shown that about half of the circulatingantibodies in the dromedary camel only consist of heavychains (Hamers-Casterman et al., 1993). Such heavy-chain-only antibodies are not produced in other healthymammals including rodents and humans (Nguyen et al.,2003). All this stresses the relevance to investigate theimmune system of the camel in more details.

The histology of the lymph nodes has been studied indifferent mammals including humans (Forket et al., 1977;Hadamitzky et al., 2010), bovine (Delverdier et al., 1993;

Galeottia et al., 1993; Christophe et al., 2008), goats (Faroonet al., 1989), rats (Ushiki et al., 1995), mice (Crivellato andMallardi, 1998), seals (Welsch et al., 1997) and water buf-falos (Zidan, 2008). The histology of the lymph nodes of the

ogy and

192 M. Zidan, R. Pabst / Veterinary Immunol

one humped camel was described in some studies (Taher,1963; Mosallam, 1978; Abdel-Magied et al., 2001) and theirembryology was described by Taher et al. (1989a,b). How-ever, all these studies did not describe the ultrastructureof the camel lymph node sufficiently and in none of themwas any histochemical or immunohistochemical charac-teristics of the lymph node studied in this species. Thelymph nodes have a general structure in all mammals withsome species variations (Dellman and Brown, 1981). Theseauthors stated that the lymph nodes are surrounded by acapsule and trabeculae of connective tissue, and a reticularmeshwork permeates the parenchyma. Afferent lymphvessels enter the lymph node at its periphery and efferentlymphatic vessels leave at the hilus. The parenchymaof the lymph nodes is organized as an outer cortex oflymphoid follicles and an inner medulla of medullarycords separated by lymphatic sinuses. The paracorticalarea of small lymphocytes extends between the cortexand medulla. In the pig the cortical and medullary tissuesare reversed. Williams et al. (1995) reported that the cellsof lymph nodes are arranged in regions of different den-sities and of distended cell types, with the cortex dividedinto three zones: zone one consists of loosely packedlymphocytes, macrophages and plasmacytes around theextreme periphery of the follicles. Zone two is denserand internal to zone one and composed mainly of smalllymphocytes and macrophages. Zone three comprises thegerminal center which contains large lymphoblasts, somemitosis, together with dendritic cells and macrophages.Christophe et al. (2008) showed that the bovine lymphnodes were encapsulated by connective tissue and fewsmooth muscle cells. Several trabeculae extended from thethin capsule. A small subcapsular sinus was continuouswith the trabecular sinuses. The cortex contained pri-mary and secondary follicles. The medulla organized intomedullary cords. In the paracortex diffuse aggregationsof lymphocytes were present. They added that the largestnumber of T cells was located in the paracortex and in theinterfollicular zones. Few CD3 positive cells were presentin the mantle zone. The medullary cords also containedCD3 positive cells. B lymphocytes were confined to thefollicles.

Taher (1963) and Mosallam (1978) showed that the cor-tical and medullary tissues of the lymph nodes of the onehumped camel were intermingled in a somewhat spleen-like fashion. Abdel-Magied et al. (2001) explained that theparenchyma of the dromedary camel was not defined intoa cortex, paracortex and medulla. Instead it comprisedlymphatic nodules, a nodular dense lymphoid tissue anddiffuse lymphatic tissue. The previous studies revealedthat the camel lymph node differs from those of othermammals in its structure. These studies depended on lightmicroscopic description and none of them extended tohistochemistry, immunohistochemistry or ultrastructureexcept that of Abdel-Magied et al. (2001), who includedsome ultrastructural features. Therefore, the present workaimed to study the ultrastructure of the lymph node of the

dromedary camel and describe the topography of lympho-cyte subsets as well as the acid and alkaline phosphataseactivity. These data will also throw some light on the func-tion of the lymph nodes of the camel. This may also be

Immunopathology 145 (2012) 191– 198

useful for future physiological and pathological studies (e.g.vaccination experiments).

2. Materials and methods

2.1. Lymph nodes

The specimens were obtained in the slaughter housefrom nine clinically healthy male camels (1, 5, 7, 8 and12 years of age) directly after slaughtering by bleeding todeath for human consumption. Specimens were obtainedfrom each camel from prescapular (superficial cervical),femoral (subiliac), mesenteric, mediastinal and spleniclymph nodes. Each lymph node was sectioned sagittalyinto two halves. Samples were sectioned from the differ-ent parts of each half representing the different area of thelymph node (capsule, subcapsular area, cortex, medulla andhilus). The sampled were processed as follows:

1. Small samples were fixed in 10% phosphate bufferedformaldehyde and used for routine histology andfor immunohistochemical demonstration of �-smoothmuscle actin.

2. Fresh samples were rapidly frozen in liquid nitrogen at−196 ◦C and used for histochemical and immunohisto-chemical studies.

3. Fresh samples were fixed immediately in 6% solutionof phosphate buffered glutaraldehyde (pH 7.4) at 4 ◦C(Mc-Dowell and Trump, 1976) and processed for trans-mission electron microscopical examination.

2.2. Routine histology

The fixed specimens were processed for paraffinsections. Four �m thick sections were prepared andstained using Mayer’s hematoxylin and eosin (H&E) stain,Gomori’s silver impregnation stain, Periodic acid Schiff(PAS) technique (Bancroft and Stevens, 1982) and Cross-man trichrome stain (Boeck, 1989).

2.3. Transmission electron microscopy

The fixed specimens were processed according to stan-dard techniques (Hayat, 1986).

Ultrathin sections were prepared, stained and examinedwith a Jeol 100 cx TEM at 80 Kvs.

2.4. Immunohistochemistry

Frozen sections (5 �m thick) were prepared and testedfor CD3, CD22 and MHCII: DR. For demonstration of �-smooth muscle actin paraffin sections were used.

2.5. Monoclonal antibodies

The primary monoclonal antibodies (mAbs) used in thisstudy were known for their cross reactivity with camel

leukocytes (Zidan et al., 2000) and �-smooth muscle actin(Zidan and Pabst, 2004). These mAbs include rabbit anti-human CD3 (Dako, Glostrup, Denmark) diluted 1:50, mouseanti-human �-smooth muscle actin (Dako) diluted 1:50,

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M. Zidan, R. Pabst / Veterinary Immunol

ouse antibovine CD22 (DM6) diluted 1:7 and mouse anti-ovine MHC class II: DR (VPM 54) diluted 1:10 (the latterwo antibodies were kindly provided by Dr. H.-J. Schu-erth, Immunology Unit, School of Veterinary Medicine,annover, Germany). The mAbs were diluted using phos-hate buffered saline (PBS) (125 g/l bovine serum albuminBSA), pH 7.2).

.6. Immunohistochemical staining procedures

Peroxidase anti-peroxidase (PAP) staining procedureas used for demonstration of CD3, CD22 and MHC

lass II: DR. The procedure was described elsewhereZidan et al., 2000). In brief, after incubation with dif-erent primary mAbs biotinylated mouse anti-rabbit IgGH+L) (Jackson Immunoresearch Labs, West Baltimore,SA) was applied to the sections previously treated withD3. Biotinylated goat anti-mouse IgG+IgM (H+L) (Jack-on Immunoresearch Labs) was applied to the sectionsreviously treated with CD22 and MHC class II: DR spe-ific mAbs. Peroxidase-conjugated streptavidin (Jacksonmmunoresearch Labs) was applied to the sections. The sec-ions were developed with PBS (pH 7.2) containing 0.05%.3-diamino benzidine tetrahydrochloride (Sigma–Aldrich,

eisenhofen, Germany) and 0.03% hydrogen peroxide.inally, the sections were counterstained with Mayer’sematoxylin (Merck, Darmstadt, Germany) and mounted

n faramount aqueous mounting medium (Dako). Alkaline

ig. 1. (a) Overviewof a camel lymph node shows the capsule (C) and trabeculaone. H&E stain. (b) The capsule consists of two layers: outer (O) mainly of connecrabeculae (T) are composed of connective tissue rich in smooth muscles. LF = lyayer (O) of the capsule has a few �-smooth muscle actin positive cells. The innessel. Arrow = high endothelial venule. APAAP technique. (d) The trabeculae (T) as infiltrated by �-smooth muscle actin positive cells. S = trabecular sinus. APAAP

Immunopathology 145 (2012) 191– 198 193

phosphatase anti-alkaline phosphatase (APAAP) stainingprocedure was used to demonstrate �-smooth muscleactin. The procedure was described elsewhere (Zidan andPabst, 2004). In brief, the paraffin sections were put intowater and incubated with the mAbs for 1 h, then were incu-bated with biotinylated goat anti-mouse IgG+IgM (H+L)(Jackson Immunoresearch Labs) followed by incubationwith alkaline phosphatase conjugated streptavidin (Jack-son Immunoresearch Labs). The sections were developedby incubation with a solution composed of 2 mg fastred (Sigma) + 4 ml APAAP substrate. Finally, the sectionswere counterstained with Mayer’s hematoxylin (Merck)and mounted in faramount aqueous mounting medium(Dako). Controls were performed incubating the sectionsin a medium without the primary mAbs in the previousprocedures.

2.7. Histochemistry

Frozen sections (5 �m thick) were prepared and used fordemonstration of acid and alkaline phosphatase enzymaticactivities according to standard procedures (Malaty, 1971).

3. Results

Examination of several histological sections preparedat different sectioning levels from the different areas ofcamel lymph nodes showed that, the lymph nodes of

e (T) enclosing the parenchyma. LF = lymphoid follicles. I = interfolliculartive tissue and inner (I) of connective tissue rich in smooth muscles. The

mphoid follicles. IF = interfollicular tissue. Trichrome stain. (c) The outerer layer (I) is rich in �-smooth muscle actin positive cells. L = lymphaticre rich in �-smooth muscle actin positive cells. The lymphoid follicle (LF)technique.

194 M. Zidan, R. Pabst / Veterinary Immunology and Immunopathology 145 (2012) 191– 198

Fig. 2. (a) The subcapsular sinus (S) containing fine PAS positive reticular fibers. The parenchymal lymphatic sinuses (ls) are lined with endothelial cellsresting on a PAS positive basement membrane. C = capsule. PAS technique. (b) The parenchyma is supported by a reticular network (R). The trabecula

ed by a

r fiber nsinuses

(arrow) is rich in collagen fibers. It has a trabecular artery and is surroundGomori’s stain. (c) The lymphoid follicle (LF) is enclosed within a reticula(LF) containing alkaline phosphatase positive cells. The wall of the blood

the camel were surrounded by a capsule of connectivetissue and smooth muscles. The capsule was arranged intwo layers: the outer layer was thicker and composedmainly of connective tissue and a few smooth muscles(Fig. 1a–c). This layer contained blood and lymphaticvessels. The inner layer was thinner and formed mainlyof smooth muscles with a few connective tissues amongthem. Trabeculae extended from the inner layer of thecapsule into the parenchyma dividing the lymph nodeinto incomplete lobules. These trabeculae had the samestructure as the inner layer of the capsule (Fig. 1b and d).Subcapsular lymphatic sinus extended under the capsuleand connected to trabecular lymphatic sinuses whichsurrounded the trabeculae. These sinuses were lined withendothelial cells resting on a basement membrane (Fig. 2a),and supported by a reticular fiber network (Fig. 2b). Afine network of reticular cells and fibers was observedextending through the lumen of these sinuses (Fig. 2).The parenchyma was divided into lymphoid folliclesand diffuse interfollicular lymphoid tissue (Fig. 1a andb). Lymphoid follicles with clear germinal centers wereobserved. The lymphoid follicles were distributed singlyor in small groups (two to three follicles). Each follicle wassupported by a reticular fiber network. These reticularfibers were rarely observed in the germinal centers (Fig. 2c

and d). A fine network of �-smooth muscle actin positivecells infiltrated each lymphoid follicle (Fig. 1d). The inter-follicular tissue was formed mainly of diffusely scatteredlymphoid cells. Lymphatic sinuses and high endothelial

trabecular sinus. LF = lymphoid follicles. Arrowheads = lymphatic sinuses.etwork (R). I = interfollicular zone. Gomori’s stain. (d) The lymph follicle

(arrows) is alkaline phosphatase positive.

venules extended in the interfollicular area. A fine networkof reticular cells and fibers supported the interfolliculartissue including the diffuse interfollicular lymphoid tissue,the lymphatic sinuses and the high endothelial venules.The lymphatic sinuses divided the interfollicular tissueinto lymphoid cords of irregular shapes and different sizes.These sinuses were lined with endothelial cells resting ona basement membrane. Clear gaps were observed betweenthese endothelial cells (Fig. 3a and b). Lymphocytes werethe main cellular component observed in the sinus lumen(Fig. 3c). Some macrophages were also associated with thelymphocytes. The high endothelial venules extended in theinterfollicular areas (Fig. 4a). These venules were lined withhigh endothelial cells resting on a basement membrane.Several lymphocytes were observed infiltrating the wallof these venules (Fig. 4a and b). Clear layers of �-smoothmuscle actin positive cells were observed around the highendothelial venules (Fig. 4c). The immunohistochemicalexamination revealed that CD22 positive cells (B lympho-cytes) were localized mainly in the lymphoid follicles. Afew cells were observed in the interfollicular zone (Fig. 5a).CD3 positive cells (T lymphocytes) were localized mainlyin the interfollicular region. A few cells were distributed inthe lymph follicles (Fig. 5b). MHC class II: DR was expressedby most cells of the follicles and the interfollicular region

(Fig. 5c). The histochemical investigation showed that acidphosphatase positive cells were regularly distributed inthe interfollicular zone. A few cells were localized in thelymphoid follicles (Fig. 5d). The alkaline phosphatase was

M. Zidan, R. Pabst / Veterinary Immunology and Immunopathology 145 (2012) 191– 198 195

Fig. 3. (a) Electron micrograph of a lymphatic sinus lined with dis-continuous endothelial lining (E) resting on a basement membrane.Arrows = endothelial gaps. L = lymphocytes. M = macrophage. (b) A highermagnification of the previous view showing clear gaps (arrows) locatedbetween endothelial cells (E). B = basement membrane. C = collagen fibers.(iP

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Fig. 4. (a) The high endothelial venule (H) is lined with high endothe-lial cells (E). Lymphocytes (arrows) are migrating through the wall ofthe venule. PAS technique. (b) Electron micrograph of a high endothe-lial venule lined with high endothelial cells (E) resting on a basement

c) Lymphatic sinuses (S) distributed in the interfollicular zone contain-ng lymphocytes (arrow) in the lumen. Arrowhead = basement membrane.AS technique.

bserved in the endothelium of the lymphatic sinuses andn the lymphoid follicles (Fig. 2d).

. Discussion

The present study used histological, histochemical andmmunohistochemical methods to describe the structuref camel lymph nodes. This may help in understand-ng their physiology and pathology. The identification ofymphocyte subsets and �-smooth muscle actin was car-

ied out using antibodies known for their cross reactivityith the corresponding antigen in camel tissues (Zidan

t al., 2000; Zidan and Pabst, 2004). These antibodies weresed because of the lack of specific antibodies against

membrane. L1 = lymphocytes in the lumen. L2 = migrating lymphocytes.(c) The high endothelial venules (arrows) are surrounded by a clear layerof �-smooth muscle actin positive cells. APAAP technique.

the camel antigens studied in this work. The capsule ofcamel lymph was characteristically different from otherspecies (Dellmann and Brown, 1981). It was arranged intotwo layers: an outer thicker layer of connective tissueand a few smooth muscle cells containing blood and lym-phatic vessels, and an inner thinner layer formed mainly ofsmooth muscle cells with a few connective tissues amongthem. Trabeculae rich in smooth muscles extended fromthe inner layer of the capsule into the parenchyma divid-ing the lymph node into incomplete lobules. Taher (1963)

demonstrated smooth muscle cells in the capsule of thecamel lymph node. Mosallam (1978), however, did notsee any smooth muscles, while Abdel-Magied et al. (2001)observed a few smooth muscle cells in the capsule and

196 M. Zidan, R. Pabst / Veterinary Immunology and Immunopathology 145 (2012) 191– 198

Fig. 5. (a) The CD22 positive B lymphocytes are localized mainly in the lymphoid follicles (LF). A few cells were observed in the interfollicular zone (I). PAPerfollicuicles (LFsitive ce

technique. (b) The CD3 positive T lymphocytes are found mainly in the int(c) MHC class II: DR is highly expressed on the cells of the lymphoid follpositive cells are localized mainly in the interfollicular zones (I). A few po

trabeculae of the lymph node of the camel. The currentwork depended on immunohistochemistry for the iden-tification of smooth muscle cells. This technique is moreaccurate than any special stains used in the previous stud-ies. The contraction of these muscle cells may acceleratelymphatic flow from the lymphatic sinuses to the efferentlymphatic vessel. Smooth muscle cells were also describedin the capsule of the lymph nodes of goats (Faroon et al.,1989) and seals (Welsch et al., 1997). The fine networkof reticular cells and fibers which extended through thelumen of the subcapsular and trabecular sinuses of thecamel lymph nodes was mentioned briefly by Taher (1963).Dellman and Brown (1981) speculated that this networkmight slow the lymph flow within the sinuses in order tofacilitate antigen–cell interaction as well as the phagocyticactivities of the macrophages. In agreement with Mosallam(1978) the current work revealed that the parenchyma isuniquely divided into incomplete lobules of lymph folliclesand interfollicular lymphoid tissue arranged into lymphoidcords of irregular shapes and different sizes. Therefore,the nodal parenchyma in the camel was characteristicallynot defined as cortex, paracortex and medulla. Taher et al.(1989b) described the developing lymph nodules in thecamel fetus as they appeared at first as darkly basophilicpatches irregularly distributed all over the lymph node.This arrangement is unique to the camel and differs from

other species, in which the lymph node is divided intothe cortex containing the lymph follicles and the medullacontaining medullary cords and free of any follicles. Thisarrangement may be more effective in filtration of lymph.

lar zone (I). A few cells are seen in the lymph follicles (LF). PAP technique.) and in the interfollicular zone (I). PAP technique. (d) Acid phosphatasells are seen in the lymphoid follicles (LF).

The secondary follicles were widely distributed in all lymphnodes, the development of several secondary lymphoid fol-licles is explained by the exposure of the camel to unlimitednumber of antigens by ingestion or inhalation or any otherroute from the surrounding environment. The presenceof secondary lymphoid follicles in the lymph node indi-cates their role in lymphocyte and antibody production asa response to antigenic stimulation (Dellman and Brown,1981). A fine network of �-smooth muscle actin positivecells was observed around the lymphoid follicles. Thesecells were described in human spleen as myofibroblasticcells (Steiniger et al., 1997). In general these �-smoothmuscle actin positive cells are able to contract after sympa-thetic stimulation (Schaffner et al., 1985). High endothelialvenules extended in the interfollicular areas. This arrange-ment is different from that of other species, in which thehigh endothelial venules are located in the paracorticalareas (Williams et al., 1995). Lymphocytes, which formpart of the recirculating pool, migrate across the wall ofthese venules from the blood to the lymph node (Gowansand Knight, 1964; Anderson and Anderson, 1976). In thepresent study, several lymphocytes were observed migrat-ing through the wall of the high endothelial venules. Thismay suggest the role of the high endothelial venules in lym-phocyte recirculation in the camel lymph node. Williamset al. (1995) reported that lymphocytes of the blood recir-

culate through the lymph nodes by migration through thecuboidal endothelium lining the high endothelial venulesand are filtered again into the lymphatic sinuses to theefferent lymphatic vessel. In agreement with Crivellato and

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M. Zidan, R. Pabst / Veterinary Immunol

allardi (1998) and Abdel-Magied et al. (2001), the currentork describes that clear gaps were observed between the

ndothelial cells lining the wall of lymphatic sinuses of thenterfollicular area. This finding differs from that of Tahert al. (1989a), who argued that the endothelial lining ofhese sinuses was probably continuous. Recirculating lym-hocytes may enter the lymphatic sinuses through these

nter-endothelial gaps.The immunohistochemical examination revealed that

D22 positive cells (B lymphocytes) were localized mainlyn the lymphoid follicles. It is well established that theymphoid follicles in the lymph node of different mam-

als are composed mainly of B lymphocytes (Dellman andrown, 1981) and that B-lymphocytes are involved in theroduction of humoral antibodies in response to antigentimulation.

T-lymphocytes are localized mainly in the interfollicu-ar area in the camel lymph node. The interfollicular areaf the camel is similar to the paracortical area of otherammals described previously, e.g. by Dellman and Brown

1981), consisting of T cells and high endothelial venules.herefore, the interfollicular area of camel lymph nodess probably equivalent to the paracortical area of other

ammalian lymph nodes. The few T cells distributed inhe lymph follicles may act as regulatory cells in B cellependent areas (Delverdier et al., 1996). These might be Telper cells as in other species. MHC class II: DR was widelyxpressed in the camel lymph node. Baldwin et al. (1986)eported that the bovine MHC class II: DR was expressedy some monocytes, macrophages, B cells and T cell blasts.herefore, this antigen may be expressed by similar cellsn the camel. In general, the cellular composition of theamel lymph node is similar to that of other species, buthe topography of T lymphocytes is unique to the camelymph node, as they are distributed in the interfollicu-ar zone instead of the paracortical area, the subcapsularnd mantel zone in other species (Dellman and Brown,981). The acid phosphatase positive cells (macrophages)ere regularly distributed in the interfollicular zone. A few

ells were localized in the lymph follicles. Abdel-Magiedt al. (2001) found macrophages in the interfollicular zone.aher et al. (1989b) demonstrated that the macrophagesre distributed in the non-follicular parenchyma of theeveloping lymph nodes of the camel. These macrophageseem to play an important role in phagocytosing foreignntigen and apoptotic lymphocytes. The few macrophagesresent in the lymphoid follicles might ingest apoptotic

ymphocytes. Zidan and Pabst (2002) observed numer-us apoptotic cells in the lymphoid follicles of camelymph nodes. Alkaline phosphatase was observed in thendothelium of the sinuses. Pearse (1958) reported thathe vascular endothelial cells of small blood vessels con-ain alkaline phosphatase which helps in active transport.ome cells in the lymphoid follicles also express alka-ine phosphatase. Mosbach-Ozmen et al. (1986) mentionedhat alkaline phosphatase is a marker of activated Bymphocytes.

onflict of interest statement

Both authors declare that there is no conflict of interest.

Immunopathology 145 (2012) 191– 198 197

Acknowledgments

We would like to express our thanks to Dr. M. Abo Maze,director of Koom Hamada Abattoir, Behera, Egypt, for thefacilities provided to obtain the specimens and to Dr. H.-J.Schubert, Immunology Unit, School of Veterinary Medicine,Hannover, Germany, for supplying us with the mouse anti-bovine CD22 (DM6) and mouse anti-bovine MHC class II:DR (VPM54). The secretarial help of S. Buhmann and M.Peter and linguistic polishing of the manuscript by S. Frykis greatly acknowledged.

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