Histology and immunohistochemistry of the gut-associated lymphoid tissue of the eastern grey kangaroo, Macropus giganteus

Mesenteric lymph nodes and gut-associated lymphoid tissue (GALT) from juvenile eastern grey kangaroos were investigated. The mesenteric nodes had a similar structure to that described for eutherian mammals. They contained distinct regions of medulla and cortex, with prominent follicles and germinal centres. Gut associated lymphoid tissue consisted of areas of submucosal follicles. These varied from areas of densely packed lymphocytes with darkly staining, prominent coronas to areas with no defined follicles. The distribution of T cells in these tissues was documented by use of species-crossreactive antibodies to the surface markers CD3 and CD5; B cells were identified by antibodies to CD79b. Within the lymph nodes T cells were located mainly in the paracortex and cortex, with limited numbers observed in the follicles; B cells were located on the marginal zone of the follicles. In GALT, T cells were located in the peripheral regions of the germinal centres of secondary follicles, while B cells were abundant in primary follicles. These observations are consistent with those made in a range of other marsupials (metatherian) and eutherian mammals and are indicative of the capacity to respond to antigens entering via the mouth.     

Endometrial lymphoid tissue: an immunohistological study.

Lymphoid tissue of the endometrium was analysed by histological, immunohistological, and electron microscopical methods in 10 healthy uteri. A panel of monoclonal antibodies recognising macrophages (OKMI), HLA-DR antigen, B lymphocytes, T lymphocytes and their subsets, and dendritic reticulum cells was used in a two stage indirect immunoperoxidase labelling technique. Endometrial lymphoid tissue showed a remarkably consistent pattern of labelling in all cases. Lymphoid tissue was present in three sites: namely, (i) intraepithelial lymphocytes (predominantly T lymphocytes with occasional macrophages) associated with periglandular and sub-epithelial HLA-DR+, OKMI+ macrophages; (ii) interstitial lymphocytes and macrophages; (iii) lymphoid aggregates in the stratum basalis. These were composed mainly of T lymphocytes with a few B lymphocytes. Dendritic reticulum cells were found in those occasional lymphoid aggregates in which germinal centres were present. These features suggest that endometrial lymphoid tissue has many of the hallmarks of mucosal associated lymphoid tissue as found elsewhere in the body--for example, the bronchus and intestine. Endometrial lymphoid tissue appears to be unique, however, in that most of the stratum functionalis in which it is situated shows cyclical shedding during the menstrual cycle.     

肺黏膜相关淋巴组织边缘区B细胞淋巴瘤及良性淋巴组织增生性疾病的临床病理分析

目的 研究肺原发性黏膜相关淋巴组织边缘区B细胞(MALT)淋巴瘤及良性淋巴组织增生性疾病的临床病理形态、免疫组织化学表型和B细胞重链基因重排,比较肺MALT淋巴瘤和良性淋巴组织增生性疾病的差异.方法 回顾性的分析原发性肺MALT淋巴瘤13例,7例肺良性淋巴组织增生性疾病资料.对标本行常规HE染色,EnVision免疫组织化学染色(抗体包括AE1/AE3、CD20、CD79α、CD3、CD5、CD10、CD21、bel-2、bcl-6、cyclinD-1)及免疫球蛋白重链IgH基因重排检测.结果 13例肺MALT淋巴瘤,细胞成分多样,分别由不同比例的小淋巴细胞样细胞、中心细胞样细胞、单核样B细胞组成,常伴有浆细胞分化.肿瘤细胞以弥漫性和滤泡边缘区排列为主,常见反应性淋巴滤泡和滤泡中心的植入.肿瘤细胞呈串珠状直接侵犯肺泡间隔和沿支气管血管束向周边及肺膜扩散.MALT淋巴瘤中,均未见坏死.9例可见肿瘤细胞侵犯血管壁,6例可见胸膜累及,2例肺门淋巴结侵犯.9例肺MALT淋巴瘤可见淋巴上皮样病变,免疫组织化学显示上皮细胞内的淋巴细胞CD20阳性,CD3阴性.7例肺良性淋巴组织增生性疾病,2例可见淋巴上皮样病变,免疫组织化学显示,其淋巴上皮样病变内的淋巴细胞,部分CD20阳性,部分CD3阳性.9例肺MALT淋巴瘤进行了免疫球蛋白重链IgH基因重排,8例阳性;7例良性淋巴组织增生性疾病均为阴性.结论 肺MALT淋巴瘤在细胞组成和排列上与其他部位结外MALT淋巴瘤相同,肿瘤细胞呈串珠状直接侵犯肺泡间隔和沿支气管血管束向周边及肺膜扩散.在肺内淋巴上皮样病变常见于MALT淋巴瘤,并有助于诊断,但并非其特异性病变,一些肺的反应性淋巴组织增生也可出现,用免疫组织化学有助于区别两种病变.免疫球蛋白重链IgH基因重排可以帮助鉴别肺MALT淋巴瘤和良性淋巴组织增生性疾病.     

Monoclonal small (well-differentiated) lymphocytic proliferations of the gastrointestinal tract resembling lymphoid hyperplasia: A neoplasm of uncertain malignant potential

Three histologically benign-appearing or diagnostically equivocal small lymphocytic proliferations of the gastrointestinal tract were examined by fresh-frozen section immunohistologic techniques. In one case, a dense infiltrate in the small intestine, consisting of small lymphocytes with round nuclei, was limited almost entirely to the mucosa. In another case, a localized colonic polyp was formed by mucosal and submucosal lobules of benign-appearing lymphoid aggregates with centrally located germinal centers. The third case, a penetrating gastric ulcer, was surrounded by histologically hyperplastic lymphoid tissue which included germinal centers. The small lymphocytes in all three cases were strongly positive for B-cell-associated antigens (B1, B2, BA-1), and all exhibited monoclonal light-chain restriction. Even though treatment consisted only of surgical resection of the lesions, no patient has had progressive disease during follow-up periods ranging from 24 to more than 50 months. We believe that the infiltrates in these cases are analogous to the morphologically benign monoclonal small lymphocytic proliferations common to the lung and orbit and that they have an uncertain, but probably low, malignant potential.     

Avian lymph node: Light and electron microscopic study

We have observed by light and transmission electron microscopy lymphoid accumulations (LA) in the chicken located along the posterior tibial-popliteal and lower femoral veins. Three types of LA were characterized: (1) LA on the wall of the lymphatic, (2) LA with germinal center, and (3) well-developed LA possessing germinal centers and an intricate lymphatic sinus system. The latter will be termed a lymph node and is perhaps the structure responding to foot-pad injection of antigen and/or phytohemagglutinin (PHA). After the injection of PHA into the foot-pad, the lymph node enlarged and revealed the intermingling of two distinct groups of cells consisting of either small lymphocytes or medium lymphocytes and lymphoblasts. Because our earlier immunological paper proved the presence of T and B cells in the node, the two histologically distinct groups of cells appearing after PHA injection could reflect compartmentalization of T and B cells in the avian lymph node. Lymphoid and adipose tissues are in the same compartment. After PHA or antigen injection into the foot pad, the lymphoid tissue proliferates and the amount of the adipose tissue rapidly decreases. This suggests that lymphoid and adipose tissue form a special complex which is separated from the surrounding tissue by delicate connective tissue capsule. The relationship of the lymphoid and adipose tissue is comparable with that of myeloid and adipose tissue in the bone marrow. The majority of the sinuses shows smooth endothelial lining while others contain “hairy” macrophages attached to the endothelium. The germinal centers are located at the periphery of the node, but a few occur inside. The cellular content of the germinal centers is not unusual except for the presence of plasma cells.     

Extra medullary Plasmacytoma of the Thyroid, Associated with Follicular Colonization and Stromal Deposition of Polytypic Immunoglobulins and Major Histocompatibility Antigens Possible Categorization in MALT Lymphoma

A 78 year old woman complaining of a neck mass underwent right hemithyroidectomy. The 7×6 cm thyroid tumor consisted predominantly of mildly atypical, epithelial membrane antigen-positive plasma cells and scattered lymphoid follicles. Features of follicular colonization (plasma cell infiltration into germinal centers) were noted. Numerous CD45RO-positive reactive T cells and a smaller number of CD2O-positive blast-like B cells were also distributed among the plasma cell infiltrate. IgG, x-type mono-clonality with J-chain reactivity was identifled in the plasma cells, including those in the lymphoid follicles. The association of pre-existing lymphocytic thyroiditis was confirmed histologically in the non-tumorous thyroid tissue. The tumor exhibited deposition of reticulin flber-rich, amorphous eosinophilic substances, provoking pronounced foreign body reactions. The deposit, polytypically im-munoreactive for immunoglobulin γ-,μ-, ϰ- and Λ chains, β₂-microglobulin and HLA-DR, was scarcely reactive upon amyloid staining, and consisted ultrastructurally of electron-dense, non-fibrillar material and entrapped collagen fibers. Multiple myeloma was ruled out by laboratory, histologic and clinical examinations. The possible categorization of this extramedullary plasmacytoma of the thyroid within low-grade B cell lymphoma of the mucosa associated lymphoid tissue (MALT) is discussed. Acta Pathol Jpn 42: 672–683, 1992.     

Two monoclonal antibodies raised against a Burkitt lymphoma cell line recognise different cell types within lymphoid follicles.

Monoclonal antibodies were raised against a laboratory derived variant of the Raji Burkitt lymphoma cell line. We have characterized two of these antibodies by screening on haematopoietic cell lines, and frozen sections of both reactive and neoplastic lymphoid tissue, and found reactivity with separate cellular components of lymphoid follicles. Monoclonal FW37.4.D5 reacts in section specifically with follicular dendritic reticular cells. Monoclonal 35.1C5 reacts with a subpopulation of splenic marginal zone, and lymph node mantle zone, B lymphocytes, but stains only rare cells within germinal centres. This monoclonal is operationally B lymphocyte specific, distinguishing an 'intermediate' B cell subset, represented in lymphoma by B chronic lymphocytic leukaemia, B hairy cell leukaemia and centrocytic lymphoma.     

Phenotypically distinct subpopulations of T cells in domes and M-cell pockets of rabbit gut-associated lymphoid tissues.

Follicle epithelium and domes of gut-associated lymphoid tissue (GALT) contain populations of lymphocytes which first contact antigen taken up from the intestine. In order to study the association of lymphocytes with M cells in follicle epithelium, monoclonal antibodies (mAb) were generated by immunizing BALB/c mice with lymphocytes populating GALT domes from NZW rabbits, and their specificity was assessed by immunohistochemistry and flow cytometry. mAb 3C10 (IgM) and 3B6 (IgG3) recognized subpopulations of intraepithelial lymphocytes associated with M cells. mAb 3C10 also identified macrophage-lymphocyte clusters in domes and tangible body macrophages in germinal centres of GALT but did not react with cells in T-dependent areas (TDA) or B cells in follicles. mAb 3B6 recognized lymphocytes in domes and B cells in follicles but not T cells in TDA of GALT. The distribution of 3B6+ cells overlapped with, but was more restricted than, that of Ia+ cells. Analysis of lymphocytes in follicle epithelium showed that greater than 95% of lymphocytes associated with M cells were Ia+. T cells represented approximately 95% of intraepithelial lymphocytes in the appendix and approximately 65% in Peyer's patches. A majority of intraepithelial lymphocytes was recognized by mAb 3B6, but mAb 3C10 identified only approximately 30%. Because neither 3C10 nor 3B6 recognized lymphocytes in TDA of GALT, these results indicate that most lymphocytes associated with M cells are a distinct phenotype of Ia+ T cells.     

Lymphatics and lymphoid tissue of the fallopian tube: immunoelectronmicroscopic study

Lymphoid tissue of the human fallopian tube consists of follicles, lymphoepithelium, and lymphatic and blood capillaries and is located consistently in the interstitial part of the human fallopian tube. Using an immunoelectronmicroscopic technique, we have elucidated the ultrastructure of the lymphoid tissue of the human fallopian tube and the fine distribution and ultrastructure of the lymphatics associated with the rabbit fallopian tube. Lymphatic capillaries arise in the lamina propria mucosa and the periphery of follicles, where they are sparsely distributed, run through the muscular layer, and form a dense network in the subserosa. Characteristic features of the ultrastructure are aggregations of smooth muscle cells, alternating areas of densely and sparsely distributed collagen fibers, and unmyelinated nerve fibers beneath the lymphatic endothelium. Immunoelectronmicroscopic analysis has demonstrated an obvious difference in the distribution of T- and B-lymphocytes in the lymphoid tissue of the human fallopian tube. Many T-lymphocytes are present in the follicles and epithelium, but B-lymphocytes are either absent or rarely found. T-lymphocytes sometimes infiltrate into the basal lamina of the epithelium lying in close contact with the follicles. We conclude that the lymphoid tissue is constantly located in the interstitial part of the human fallopian tube and that intraepithelial lymphocytes, mainly T-lymphocytes, migrate via the basal lamina of the epithelium from follicles. Lymphatic capillaries in the fallopian tube may be the main migratory route of intraepithelial lymphocytes. The intraepithelial lymphocytes and epithelial cells of the fallopian tube have attracted considerable interest as a result of immunological studies of the recognition of spermatozoal antigens and the fertilized ovum.(ABSTRACT TRUNCATED AT 250 WORDS)     

大鼠腘窝淋巴结内淋巴滤泡的生后发育

目的:研究大鼠淋巴结淋巴滤泡的生后发育.方法:采用常规组织学、免疫细胞化学及三维重建技术研究了大鼠腘窝淋巴结内淋巴滤泡的发生.结果:生后18天始,淋巴结浅层皮质内sIgM阳性B淋巴细胞聚集形成初级淋巴滤泡.生后3周ED-5阳性滤泡树突状细胞出现.随着鼠龄及体重的增长,初级淋巴滤泡不断扩大,每个淋巴结内淋巴滤泡数亦增多.生后13周滤泡数达高峰,平均每个淋巴结86个,13周以后体重缓慢增长,淋巴滤泡数逐渐下降.生后8周时,次级淋巴滤泡出现,ED-5阳性滤泡树突状细胞主要分布于亮区.结论:初级淋巴滤泡形成过程中B淋巴细胞聚集可能诱导局部网状细胞分化成滤泡树突状细胞;发育期间淋巴滤泡数随体重增长而增加可能与某些决定机体生长的因素作用有关.     

NON-HODGKIN MALIGNANT LYMPHOMA WITH SPECIAL REFERENCE TO DESMOSOME-LIKE JUNCTIONS

Seventy-nine cases of non-Hodgkin malignant lymphoma were light and electron microscopically evaluated with special reference to intercellular correlationship comparing with non-neoplastic lymph nodal cells and cultured B cells. Reticulum cells and histiocytes are regarded as an independent cell unit. Reticulum cell sarcoma shows a fibrosarcomatous proliferation with abundant reticulin fibers, while histiocytic sarcoma is confined to a pleomorphic neoplasm with valid phagocytization. Lymphoid cells are divided into large, intermediate and small lymphocytes. Under inflammation and cultivation they, especially intermediate and large, preferentially proliferated clustering in a reticular fashion, which are designated as reticular lymphocytes, in contrast with nonreticular lymphocytes individually separated. The desmosome-like junctions are found among reticular lymphocytes not only in but also outside germinal centers as well as in vessels and among cultured B cells. Lymphocytic sarcomas, either nodular or diffuse, are classified into reticular and nonreticular types in association with their cellular sizes. The desmosome-like junctions are predisposedly disclosed in reticular lymphoma irrespective of proliferating patterns, nodular or diffuse, and of membrane character, B or T. And the junctions are not regarded as a hallmark for follicular or nodular lymphomas of germinal center cell origin.     

Age-Associated Changes in the Cellular Composition of the Human Adenoid

Histological investigations suggest that the size and number of lymphoid follicles of the adenoids and tonsils decrease during ageing. The mechanisms underlying the histological changes are unknown. The authors have analysed the frequency of lymphocyte subpopulations in the adenoids by flow cytometry. The proportion of B lymphocytes decreased and the proportion of T lymphocytes of all mononuclear cells increased with age. Of all B lymphocytes the proportion of CD38⁺, surface IgD⁻ B lymphocytes representing the germinal centre cell phenotype, decreased and the proportion of CD38⁻, IgD⁻ B lymphocytes representing the mature B lymphocyte phenotype, increased with age. The expression of CD23, a cell surface molecule associated with activation of follicular mantle IgD⁺ B lymphocytes, did not change with increasing age. The results imply that the involution of the adenoid is associated with a decreased germinal centre reaction and relative accumulation of mature B cells in the adenoidal tissue, as analysed by three-colour flow cytometry.     

Human Germinal Centre B Cells Inhibit Mitogen-Induced proliferation of Mantle Zone B Cells

Lymphoid follicles are the main B-cell areas in peripheral lymphoid tissues. These structures commonly consist of germinal centre (GC) and mantle zone (MZ) regions. In the present work, human tonsillar B cells belonging to these two compartments were purified by a combination of density centrifugation and separation techniques involving the recognition by monoclonal antibodies of specific surface molecules followed by panning and magnetic bead selection. These purified populations were identified as GC and MZ cells by three different criteria: (1) GC cells showed the phenotype IgD- CD20+bright CD38+ CD44- and peanut agglutinin (PNA)+, and MZ cells were IgD+ CD20+dim CD38- CD44+ and PNA-; (2) morphologically, MZ cells appeared as small resting lymphocytes whereas GC cells consisted of large blastic cells of the germinal centre; (3) functionally, most GC, but not MZ, cells underwent apoptosis early in culture. The isolation of GC and MZ cells allowed the study of their proliferative response. As a result of these studies, GC cells were demonstrated to inhibit the proliferation of MZ cells in response to B-cell mitogens (Staphylococcus aureus Cowan I and anti-mu plus BCGF) in a concentration-dependent way; 50% inhibition was reached at a GC/MZ cell ratio of 1/2. This effect did not require GC-cell DNA synthesis since similar results were obtained with irradiated GC cells. Neither was it due to a non-specific toxic effect since GC cells did not alter the proliferative response of autologous T cells to mitogens (phytohaemagglutin and anti-CD3). The inhibition required cellular contact between GC and MZ cells, and was not restricted by histocompatibility barriers. These data suggest the possible existence of a new regulatory pathway within peripheral B-cell areas.     

Immunohistochemical analysis of ageing human B and T cell populations reveals an age-related decline of CD8 T cells in spleen but not gut-associated lymphoid tissue (GALT)

It is thought that senescence of the immune system is responsible, at least in part, for many health problems associated with ageing. Previous studies on changes in lymphocyte composition have used flow cytometry to study peripheral blood lymphocytes (PBL's), or cells isolated from rodent tissue, and have yielded conflicting results. We have used immunohistochemistry to determine whether the B and T cells in human tissue from spleen and gut are affected by age. Areas of germinal centre, mantle zone and marginal zone of B cell follicles were measured. In addition, CD4 and CD8 T cells in T cell areas and in B cell follicles were counted. We observed a striking age-related decrease in the proportion of CD8+ T cells in the T cell zones of the spleen. This decrease was not apparent in the T cell population that occupies splenic B cell areas, or in GALT. Further differences, in CD4+ cells, were seen between T cell populations in the T cell zones and those in B cell areas. These findings highlight differences between lymphocyte populations in different lymphoid tissues, and different compartments within each tissue, which may be of importance in future studies of the ageing immune system.     

Detection of ectopic B-cell follicles with germinal centers in the meninges of patients with secondary progressive multiple sclerosis

Multiple sclerosis (MS) is characterized by synthesis of oligoclonal immunoglobulins and the presence of B-cell clonal expansions in the central nervous system (CNS). Because ectopic lymphoid tissue generated at sites of chronic inflammation is thought to be important in sustaining immunopathological processes, we have investigated whether structures resembling lymphoid follicles could be identified in the CNS of MS patients. Sections from post-mortem MS brains and spinal cords were screened using immunohistochemistry for the presence of CD20+ B-cells, CD3+ T-cells, CD138+ plasma cells and CD21+, CD35+ follicular dendritic cells, and for the expression of lymphoid chemokines (CXCL 13, CCL21) and peripheral node addressin (PNAd). Lymphoid follicle-like structures containing B-cells, T-cells and plasma cells, and a network of follicular dendritic cells producing CXCL13 were observed in the cerebral meninges of 2 out of 3 patients with secondary progressive MS, but not in relapsing remitting and primary progressive MS. We also show that proliferating B-cells are present in intrameningeal follicles, a finding which is suggestive of germinal center formation. No follicle-like structures were detected in parenchymal lesions. The formation of ectopic lymphoid follicies in the meninges of patients with MS could represent a critical step in maintaining humoral autoimmunity and in disease exacerbation.     

Human tonsil intraepithelial B cells: a marginal zone-related subpopulation.

AIMS: To determine if intraepithelial B cells in reactive human palatine tonsils were similar to the marginal zone cells of the spleen and Peyer's patches. METHODS: Reactive human palatine tonsils were studied using conventional methods of light microscopy, electron microscopy, and a panel of monoclonal antibodies for leucocyte common antigens. RESULTS: Clinically important numbers of marginal zone-related B cells around the mantle zone were absent in lymphoid follicles, but in the cryptal epithelium there were abundant lymphoid cells with centrocyte-like nuclei and clear cytoplasm, intermingled with macrophages and plasma cells. The immunophenotype of these intraepithelial B cells was distinctive and similar to that found in the splenic marginal zone cells (IgM+, IgD-, CD23-, CD10-, CD35+, CD21+, bc12+, KB61+). CONCLUSIONS: Intraepithelial B cells in human tonsil could represent the counterpart of the marginal zone described in Peyer's patches. Their presence within the epithelium could reflect the destination for the malignant B cells in the lymphoepithelial lesion of mucosa associated lymphoid tissue (MALT) lymphomas. Human palatine tonsil lymphoid tissue has morphological, immunophenotypic, and pathological features similar to those of MALT.     

Expression of the gangliosides GD3 and GD2 on lymphocytes in tissue sections of melanoma

Previous studies in vitro have shown that monoclonal antibodies (MAbs) against gangliosides GD3 and GD2 potentiate lymphocyte responses to a variety of stimuli. The purpose of the present study was to determine by immunohistological techniques whether GD3 and GD2 was expressed on lymphoid cells in vivo around melanoma cells. Studies on metastases in lymph nodes indicated that the lymphoid infiltrate around the margins of the metastases was predominantly CD4+ T cells, which were shown by dual labelling techniques to express mainly GD2 and to a lesser extent GD3. CD4+GD3+ T cells were detected more frequently in cortical regions of the lymph nodes. CD8+ T cells were less numerous than CD4+ T cells and expressed both GD3 and GD2. Expression of GD2 was also prominent on CD4+ T cells, B lymphocytes and dendritic reticular cells in germinal centres, whereas GD3 was mainly expressed on T cells in the margins of the follicles. In contrast to the predominance of CD4+ T cells in lymph nodes, CD4+ and CD8+ T cells were in approximately equal proportions about primary melanoma and metastases in skin. GD2 was largely undetectable on lymphocytes at these sites. In contrast, GD3 was detected on both CD8+ and CD4+ lymphocytes but not on B lymphocytes. The absence of GD2 on CD4+ T cells in skin suggested the latter were a different subpopulation to those in lymph nodes. There appeared to be no clear correlation, however, with subsets of CD4 T cells defined by the 2H4 and Leu 8 MAbs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical study of lymphocyte populations infiltrating the gastric mucosa of beagle dogs experimentally infected with Helicobacter pylori

Experimental infection of beagle dogs with Helicobacter pylori induces recruitment to the gastric mucosae of neutrophils at early stages and later of mononuclear cells that organize into lymphoid follicles. These structures become macroscopically evident and consist of peripheral CD4(+) T lymphocytes and central CD21(+) B lymphocytes. Furthermore, transient expression of interleukin-8 (IL-8) parallels the presence of neutrophils in the gastric mucosae, whereas expression of IL-6 tends to persist chronically.     

A PATHOLOGICAL STUDY ON EOSINOPHILIC LYMPHFOLLICULOID GRANULOMA (KIMURA'S DISEASE)

The present study Included 46 cases of eosinophilic lymphfolliculoid granuloma(Kimura's disease), which occurred mainly in males between the ages of 11 to 52 years. The common sites were the soft tissue of the head and neck region. Although recurrence was not infrequent, the clinical course was benign. Laboratory findings revealed eosinophilia and frequent elevation of serum IgE. The histological characteristics consisted of proliferation of lymphoid follicles and granulation tissue with infiltration of eosinophils, mast cells, plasma cells, lymphocytes, and histiocytes, some degree of vascular proliferation, and fibrosis. With the appliance of unlabeled peroxidase-antiperoxidase method, a marked reticular reaction of IgE was confirmed in the germinal center of the folliculoid structure, and there were quite a number of IgE producing plasma cells. Many mast cells with IgE bound to their cell surface were seen in the granulation tissue. Toluidine blue staining and electron microscopy revealed fairly well preserved granules in mast cells, being quite different from the changes seen in type I allergy.     

Ultrastructural and cytoarchitectural features of lymphoreticular organs in the colon and rectum of adult BALB/c mice

The structure and function of colonic mucosal lymphoid organs remain largely unexplored, especially in the rectum hidden within the pelvic vault. Two-month-old female BALB/c mice were anesthetized, and the entire colon was removed from cecum to anus. Distal colonic patches were then prepared for electron microscopy or were quick-frozen and sectioned for immunoperoxidase localization of B cells and T cell subsets. Aggregated lymphoid follicles were distributed irregularly along the entire colon with an average of 1.4 patches per centimeter of colon length. There were large collections of follicles opposite the ileocecal valve (cecal patches), variable numbers of patches throughout the colon, and at least one patch within 10 mm of the anus (rectal patch). Follicles were adjacent to branching crypts lined by epithelium infiltrated by lymphoid cells and containing few goblet cells. In electron micrographs, M cells were identified by their short, irregular microvilli; intraepithelial lymphoid cells; reduced lysosomal dense bodies; and an expanded tubulovesicular network. Small germinal centers were seen. Cytoarchitectural components of colonic lymphoid follicles and Peyer's patch follicles were remarkably similar, despite differences in surrounding mucosa and luminal microbial exposure. The presence of organized lymphoid tissue with M cells and germinal centers suggests that transepithelial particle transport and antigen recognition can take place in the rectum. Whether such tissue has the capacity for uptake of luminal microorganisms is of particular interest, not only because colonic follicles may be sites for local initiation of immune responses but also because they may be important entry points for systemic infection.