T-cells in follicular hyperplasia and follicular center-cell lymphomas: an immunoultrastructural study of the T-cell receptor-associated CD3 antigen

T-cells are an integral part of normal follicular centers and many follicular center-cell (FCC) lymphomas. Because the functional role of these cells remains imprecisely determined and because ultrastructural localization of the T-cell antigen receptor-associated CD3 antigen has not been previously reported, an immunoultrastructural study of four tonsils and four FCC lymphomas was performed using an anti-CD3 antibody (UCHT-1). Normal interfollicular CD3-positive T-cells always demonstrated surface membrane positivity, as did 94% of normal and 88% of neoplastic FCC-associated CD3-positive cells. Conversely, whereas only 5% of normal interfollicular CD3-positive cells showed perinuclear positivity, 58% of normal and 38% of neoplastic FCC-associated CD3-positive cells did (p less than 0.001). Definite endoplasmic reticulum (ER) staining for CD3 was identified in 4% and 8% of cells associated with normal or neoplastic FCC, respectively, but in none of the T-zone lymphocytes. Because the perinuclear space is reported to be a site of protein synthesis in cells with little ER, and because of the occasional ER staining observed in cells with perinuclear staining, perinuclear CD3 positivity probably represents CD3 synthesis in mature tonsillar T-cells. The frequency of perinuclear positivity in the FCC-associated T-cells, together with the loss of surface positivity in some cells at this site, suggests that this could represent in vivo T-cell "activation" in follicular centers, with modulation and resynthesis of the CD3 antigen. Furthermore, the results demonstrate a similar phenomenon in the T-cells associated with neoplastic follicular center cells.     

S-100 immunoreactive interdigitating cells in normal and in Down's syndrome human thymuses.

The present research deals with the localization of the interdigitating cells (IDCs) in normal and in Down's human thymuses. Eight thymic biopsy samples of normal children from 16 months to 10 1/2 years and six samples of Down's children from 2 months to 6 1/2 years were stained by the indirect immuno-peroxidase method using an anti-S-100 protein serum. IDCs are localized in the medullary zones, always numerous in all the Down's thymuses and in an age-related decreasing number in normal thymuses. The interrelationships between the physiological and pathological role of IDCs in inducing self-tolerance and T-cell activation and the numerical distribution in normal and in Down's human thymuses are discussed.     

Emperipolesis of lymphoid cells by human follicular dendritic cells in vitro.

Isolated follicular dendritic cells (FDCs) showed true and pseudoemperipolesis of fresh tonsillar lymphocytes, even after long-term (50-day) cultivation. Emperipolesis by FDCs was not restricted by allotype specificity, nor was it inhibited by the addition of antibodies against MHC-I & II antigens. Follicular dendritic cells predominantly engulfed B-cells; monocytes and macrophages were not found between FDC cytoplasmic extensions. When highly purified T-cell populations were added to FDC cultures emperipolesis of T-cells occurred, particularly those of the CD4-positive phenotype. Mitoses appeared within 6 h in the emperipolesed lymphocytes and, after an additional 18 h, some lymphocytes exhibited apoptosis.     

Phenotype and topography of human thymic B cells

Using single and double labeling immunohistochemical techniques and a large panel of monoclonal antibodies against B-cell differentiation antigens, including those newly defined at the Fourth International Leucocyte Typing Workshop, we have examined the immunophenotype and tissue distribution of human thymic B-cells. The existence of a distinct B-cell population as a constant constituent of the thymic microenvironment has been noted only recently. We found a singificant population of B-lymphocytes in the thymic medulla expressing the B-cell restricted antigens CD19, CD20, CD22, CD37, CD72, CD76 and IgM and IgD. As with other extrafollicular B-lymphocytes, they differ significantly from both follicle mantle and germinal center cells in morphology and immunophenotype, which points to alternative modes of B-cell differentiation. Thymic B-cells themselves show considerable heterogeneity and a subpopulation with dendritic features and the expression of CD23 has been referred to as “asteroid” cells. Their close association with T-cells and medullary epithelial cells points to a functional role for B-cells in the thymus. A second population of B-lymphocytes together with frequent lymph follicles is found within the extrathymic perviascular space. Though separated from the medulla by a layer of epithelial cells, a clear distinction between the B-cells of these two compartments is not always possible. The intramedullary B-cell compartment shows a parallel numeric increase with the occurrence of germinal centers in the perivascular space, mostly due to an accumulation of B-cells in the medulla adjacent to these lymph follicles. Thus a close relationship between the intra-and extramedullary B-cell population of the thymus seems likely. Presented in part in Leucocyte Typing IV (1989) Knapp W et al. (eds) Oxford University Press, Oxford, pp 221–222     

Phenotype and topography of human thymic B cells. An immunohistologic study.

Using single and double labeling immunohistochemical techniques and a large panel of monoclonal antibodies against B-cell differentiation antigens, including those newly defined at the Fourth International Leucocyte Typing Workshop, we have examined the immunophenotype and tissue distribution of human thymic B-cells. The existence of a distinct B-cell population as a constant constituent of the thymic microenvironment has been noted only recently. We found a significant population of B-lymphocytes in the thymic medulla expressing the B-cell restricted antigens CD19, CD20, CD22, CD37, CD72, CD76 and IgM and IgD. As with other extrafollicular B-lymphocytes, they differ significantly from both follicle mantle and germinal center cells in morphology and immunophenotype, which points to alternative modes of B-cell differentiation. Thymic B-cells themselves show considerable heterogeneity and a subpopulation with dendritic features and the expression of CD23 has been referred to as "asteroid" cells. Their close association with T-cells and medullary epithelial cells points to a functional role for B-cells in the thymus. A second population of B-lymphocytes together with frequent lymph follicles is found within the extrathymic perviascular space. Though separated from the medulla by a layer of epithelial cells, a clear distinction between the B-cells of these two compartments is not always possible. The intramedullary B-cell compartment shows a parallel numeric increase with the occurrence of germinal centers in the perivascular space, mostly due to an accumulation of B-cells in the medulla adjacent to these lymph follicles. Thus a close relationship between the intra- and extramedullary B-cell population of the thymus seems likely.     

Neonatal exposure to propylthiouracil induces a shift in lymphoid cell sub-populations in the developing postnatal male rat spleen and thymus

Evidence of the connections between the immune system and the thyroid axis is increasingly strong; however, much of the data are focused on immune effects of altered thyroid status in adults or rodents with congenital defects of the pituitary/thyroid axis. The object of the present study was to determine the effects of PTU-induced hypothyroidism on the developing immune system of the rat by focussing on both the spleen and thymus gland. Male Sprague-Dawley rat pups were exposed to PTU through maternal milk by giving the mothers 0.02% PTU in their drinking water starting on the pups' day of birth until day 24 (d24), shortly before weaning on d28. Animals were sampled on days 14, 22, 30, and 91. The mean body weight was decreased in the PTU-treated animals on days 14, 22, and 30. The mean spleen and thymic weights and cellularity were all decreased in the PTU-treated animals on d22 and d30. PTU exposure increased the proportion of NK cells in the spleen on days 14, 22, and 30. The proportion of T-cells was increased on days 22 and 30 with a particular increase in the CD4+ T-cells, resulting in an increase in the ratio of helper T-cells to suppressor/cytotoxic T-cells at d22. PTU also decreased the proportion of splenic B-cells at days 14, 22, and 30 which could explain the increased proportion of both NK and T-cells during these sampling periods. PTU treatment decreased the lytic ability of NK cells at d22, but no functional differences were observed at days 14, 30, 91, despite the increased proportion of NK cells in PTU-exposed animals at days 14, 22, and 30. PTU exposure also increased the proportion of CD4+CD8- cells in the thymus on d22 and caused an increase in both the CD4+CD8- and CD4-CD8+ populations on d30. These data suggest that the effects of temporary, PTU-induced hypothyroidism on the cell populations in the spleen partially result from transient changes in thymic T-cell development, including a shift towards increased CD4+CD8- cells. The data also suggest that temporary hypothyroidism early in development decreases B-cell development in a transient fashion. Temporary hypothyroidism induced from birth to the latter stages of the weaning period induced transitory effects on the spleen, thymus, and immune cell sub-populations--all of which recovered to normal values when the animals matured.     

Prognostic and Predictive Value of Tumor-infiltrating Leukocytes and of Immune Checkpoint Molecules PD1 and PDL1 in Clear Cell Renal Cell Carcinoma

INTRODUCTION: Immune checkpoint inhibitors (ICI) have been approved for patients with clear cell renal cell carcinoma (ccRCC), but not all patients benefit from ICI. One reason is the tumor microenvironment (TME) that has substantial influence on patient's prognosis and therapy response. Thus, we comprehensively analyzed the TME of ccRCC regarding prognostic and predictive properties. METHODS: Tumor-infiltrating CD3-positive T-cells, CD8-positive cytotoxic T-lymphocytes (CTLs), regulatory T-cells, B-cells, plasma cells, macrophages, granulocytes, programmed cell death receptor 1 (PD-1), and its ligand PD-L1 were examined in a large hospital-based series of ccRCC with long-term follow-up information (n = 756) and in another patient collective with information on response to nivolumab therapy (n = 8). Tissue microarray technique and digital image analysis were used. Relationship between immune cell infiltration and tumor characteristics, cancer-specific survival (CSS), or response to ICI was examined. RESULTS: Univariate survival analysis revealed that increased tumor-infiltrating B-cells, T-cells, and PD-1-positive cells were significantly associated with favorable CSS and high levels of intratumoral granulocytes, macrophages, cytotoxic T-cells, and PD-L1 significantly with poor CSS. High CTL or B-cell infiltration and high PD-L1 expression of ccRCC tumor cells qualified as independent prognostic biomarkers for patients' CSS. Significantly higher densities of intratumoral T-cells, CTLs, and PD-1-positive immune cells were observed in ccRCC with response to ICI compared with patients with mixed or no response (CD3: p = 0.003; CD8: p = 0.006; PD-1: p = 0.01). DISCUSSION: This study shows that subsets of tumor-infiltrating leukocytes in the TME and also PD-1/PD-L1 provide prognostic and predictive information for patients with ccRCC.     

Phenotypic characterization of thymic prelymphoma cells of B10 mice treated with split-dose irradiation

Using an intrathymic injection assay on B10 Thy-1 congenic mice, it was demonstrated that thymic prelymphoma cells first developed within the thymuses from 4 to 8 days after split-dose irradiation and were detected in more than 63% of the test donor thymuses when examined at 21 and 31 days after irradiation. Moreover, some mice (25%) at 2 mo after split-dose irradiation had already developed thymic lymphomas in their thymuses. To characterize these thymic prelymphoma cells, the thymocytes from B10 Thy-1.1 mice 1 mo after irradiation were stained with anti-CD4 and anti-CD8 mAb and were sorted into four subpopulations. These fractionated cells were injected into the recipient thymuses to examine which subpopulation contained thymic prelymphoma cells. The results indicated that thymic prelymphoma cells existed mainly in CD4- CD8- and CD4- CD8+ thymocyte subpopulations and also in CD4+ CD8+ subpopulation. T cell lymphomas derived from CD4- CD8- prelymphoma cells had mainly CD4- CD8- or CD4- CD8+ phenotypes. T cell lymphomas developed from CD4- CD8+ prelymphoma cells mainly expressed CD4- CD8+ or CD4+ CD8+ phenotype. T cell lymphomas originating from CD4+ CD8+ prelymphoma cells were mainly CD4+ CD8+ but some CD4- CD8+ or CD4+ CD8- cells were also present. These thymic prelymphoma cells were further characterized phenotypically in relation to their expression of the marker defined by the mAb against J11d marker and TL-2 (thymus-leukemia) Ag, which is not expressed on normal thymocytes of B10.Thy-1.2 or B10.Thy-1.1 strain, but appears on the thymocytes of lymphomagenic irradiated mice. The results indicated that the prelymphoma cells existed in J11d+, TL-2+ cells.     

Differential DNA damage induced by H2O2 and bleomycin in subpopulations of human white blood cells

The purpose of this study was to characterize the differential sensitivities of various subpopulations of human white blood cells after exposure to H2O2 (an oxidant agent) and bleomycin (a radiomimetic glycopeptide), in vitro, using single-cell gel electrophoresis (SCGE). Human peripheral blood was fractionated into mononuclear cells, which were further separated into monocytes, CD4+ T-cells, CD8+ T-cells, B-cells and natural killer cells (NK cells). The separated fractions were exposed to different doses of H2O2 and bleomycin, and then used to measure levels of induced and basal DNA damage. There was a significant increase in the amount of DNA damage in CD4+ T-cells, CD8+ T-cells, NK cells and B-cells when treated with H2O2 and bleomycin, whereas monocytes had the lowest sensitivity to H2O2 compared with the other cell fractions, but no lower sensitivity to bleomycin. Furthermore, CD4+ T-cells and CD8+ T-cells had the highest levels of basal DNA damage. When basal DNA damage was taken into account, NK cells tended to show a higher sensitivity to H2O2 than CD4+ T-cells, CD8+ T-cells and monocytes. In addition, B-cells, which showed lower sensitivity to H2O2 than CD4+ T-cells, CD8+ T-cells and NK cells when exposed to lower doses of H2O2 (<10 microM), showed higher sensitivity to H2O2 at higher doses (>20 microM). On the other hand, B-cells showed the highest sensitivity to bleomycin.     

Proliferating cells in histiocytic necrotizing lymphadenitis

The phenotypes of proliferating cells in histiocytic necrotizing lymphadenitis (HNL) were examined. The affected areas consisted mainly of CD 8-positive (suppressor/cytotoxic T-cells) and CD 4-positive (helper/inducer T-cells) in association with some CD 15-positive cells (monocytes). A marker of proliferating cells (Ki-67) and monoclonal antibodies for determining the phenotypes of cells (CD 4, CD 8, CD 15) in the affected areas were applied using a double-staining method. Ki-67-positive proliferating cells were mainly CD 8-positive. A few CD 4-positive cells and rare CD 15-positive cells were also Ki-67-positive. The percentage of CD 8-positive cells increased gradually over time and the ratio of CD 8-positive to proliferating cells did not decrease throughout the observation period of 6 weeks. These results suggest that the proliferation of CD 8-positive T-cells together with the accumulation of CD 4- and CD 15-positive cells is the main phenomenon occurring in HNL.     

Proliferating cells in histiocytic necrotizing lymphadenitis.

The phenotypes of proliferating cells in histiocytic necrotizing lymphadenitis (HNL) were examined. The affected areas consisted mainly of CD 8-positive (suppressor/cytotoxic T-cells) and CD 4-positive (helper/inducer T-cells) in association with some CD 15-positive cells (monocytes). A marker of proliferating cells (Ki-67) and monoclonal antibodies for determining the phenotypes of cells (CD 4, CD 8, CD 15) in the affected areas were applied using a double-staining method. Ki-67-positive proliferating cells were mainly CD 8-positive. A few CD 4-positive cells and rare CD 15-positive cells were also Ki-67-positive. The percentage of CD 8-positive cells increased gradually over time and the ratio of CD 8-positive to proliferating cells did not decrease throughout the observation period of 6 weeks. These results suggest that the proliferation of CD 8-positive T-cells together with the accumulation of CD 4- and CD 15-positive cells is the main phenomenon occurring in HNL.     

Differential apoptotic response to ionizing radiation in subpopulations of human white blood cells.

The purpose of this paper is to characterize the apoptotic response of various subpopulations of human white blood cells after in vitro exposure to ionizing radiation using the modified neutral comet assay (MNCA). White blood cells, isolated from human whole blood, were fractionated into granulocytes and mononuclear cells which were further separated into B-cells, natural killer (NK) cells, and CD4(+) and CD8(+) T-cells. The separated fractions were exposed to low doses of X-rays and then MNCA was used to measure the apoptotic fraction (AF) at different time points in irradiated and unirradiated aliquots of sorted cultures. The spontaneous AF in unirradiated control cells was the most critical determinant of whether an apoptotic response could be detected in irradiated cells. When cultured in isolation granulocytes and B-cells had the highest background AF, with NK cells having the next highest. CD4(+) and CD8(+) T-cells had a low, stable, spontaneous AF which gave them the highest signal-to-noise ratio. Although B-cells demonstrated the highest radiation-induced apoptotic response to 1Gy of X-rays, CD8(+) T-cells were the most radiation-responsive lymphocytes due to their low spontaneous AF. By generating dose response curves for CD4(+) and CD8(+) T-cells, the sensitivity of the MNCA for detecting apoptosis in these two cell types was also examined.     

Immunohistochemical studies on a human thymic epithelial cell subset defined by the anti-cytokeratin 18 monoclonal antibody

Summary Two monoclonal antibodies respectively recognizing cytokeratins (CK) 18 and 19 were applied to the human thymic epithelium (in vivo and in vitro) in normal and pathological conditions, including 12 thymomas. We observed that in both normal and hyperplastic thymuses (from patients with myasthenia gravis) virtually the entire epithelial network was CK19-positive as were the majority of cells growing in culture. In four thymomas, however, the expression of cytokeratin 19 was not detected by immunofluorescence. On the other hand, CK18 was expressed by a discrete subset of medullary thymic epithelial cells in normal and in hyperplastic thymuses. Among the thymomas a large majority was either negative or contained few isolated CK18-positive cells scattered within the tumour. Conversely, in the two undifferentiated epithelial thymomas, virtually all the tumoral network was strongly labeled with the anti-CK18 monoclonal antibody. The present investigation thus not only defines the human thymic epithelial cell subset on the basis of differential cytokeratin expression but also indicates that anti-CK antibodies with single cytokeratin specificities can be regarded as useful tools to study the heterogeneity of thymomas.     

CD80 and CD86 Differentially Regulate Mechanical Interactions of T-Cells with Antigen-Presenting Dendritic Cells and B-Cells

Functional T-cell responses are initiated by physical interactions between T-cells and antigen-presenting cells (APCs), including dendritic cells (DCs) and B-cells. T-cells are activated more effectively by DCs than by B-cells, but little is known about the key molecular mechanisms that underpin the particular potency of DC in triggering T-cell responses. To better understand the influence of physical intercellular interactions on APC efficacy in activating T-cells, we used single cell force spectroscopy to characterize and compare the mechanical forces of interactions between DC:T-cells and B:T-cells. Following antigen stimulation, intercellular interactions of DC:T-cell conjugates were stronger than B:T-cell interactions. DCs induced higher levels of T-cell calcium mobilization and production of IL-2 and IFNγ than were elicited by B-cells, thus suggesting that tight intercellular contacts are important in providing mechanically stable environment to initiate T-cell activation. Blocking antibodies targeting surface co-stimulatory molecules CD80 or CD86 weakened intercellular interactions and dampen T-cell activation, highlighting the amplificatory roles of CD80/86 in regulating APC:T-cell interactions and T-cell functional activation. The variable strength of mechanical forces between DC:T-cells and B:T-cell interactions were not solely dependent on differential APC expression of CD80/86, since DCs were superior to B-cells in promoting strong interactions with T-cells even when CD80 and CD86 were inhibited. These data provide mechanical insights into the effects of co-stimulatory molecules in regulating APC:T-cell interactions.     

Enzyme and immunohistochemistry of follicular hyperplasia in AIDS-related lymphadenopathy

We used a panel of monoclonal and polyclonal antibodies to analyze frozen and paraffin-embedded lymph node biopsy specimens from 25 intravenous drug abusers (IVDA) with acquired immunodeficiency syndrome (AIDS)-related lymphadenopathy histologically characterized by follicular hyperplasia. Our aim was to obtain diagnostic clues to this commonly occurring pattern. Double-labelling immunohistological studies were also performed on selected frozen sections and 13 plastic-embedded specimens were tested by a number of enzyme reactions. Consistent features in IVDA included abnormally high numbers of intrafollicular T-cells, positive for acid phosphatase and beta-glucuronidase, most of which had Leu-2a-positive phenotype; a marked reduction or loss of mantle zone B-cells (positive for surface IgD-IgM and alkaline phosphatase); and disarray of the network of follicular dendritic reticulum cells (DRCs), as revealed with DRC-1 and anti-S-100 protein antibodies or with reaction for 5'-nucleotidase. When present, distinctive intrafollicular clusters of Leu-2a-positive T-cells and mantle zone B-cells were nearly always associated with areas lacking DRCs in some patients. The intrafollicular hypervascularity invariably found in IVDA proved to be of a true capillary nature, as demonstrated by alkaline phosphatase, 5'-nucleotidase, and ATPase reactions. In control tissues, all showing absence of Leu-2a-positive intrafollicular T-cells, most of the above individual changes could be detected, although they were occasional, mild, and never associated within the same follicle. By contrast, combined immunohistological and enzyme histochemical findings in IVDA indicated that in most follicles such changes were marked and very often associated within the same follicle in each case.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lymphocyte populations of non-scleronodular Hodgkin's disease subtypes in different stages of lymphocyte depletion. An immunophenotypic and quantitative study

Twenty-one cases of non-scleronodular Hodgkin's disease with variable lymphocyte contents were studied immunophenotypically and quantitatively to analyse the distribution of different lymphocyte populations and to determine whether selective loss of lymphocyte subpopulations accompanies overall lymphocyte depletion. In Hodgkin's tissue B-cells were scanty and unevenly distributed in samples with both many and few lymphocytes. Several large B, LN1-positive (possibly activated) cells were observed in a few cases. CD3-positive T-lymphocytes predominated in all cases; the same cells were also UCHL1-positive, thus expressing characteristics of mature T-memory cells. CD4-positive lymphocytes were usually more numerous than CD8-positive lymphocytes, but quantitative evaluation of the latter showed that they did not decrease in proportion to any diminution of the whole lymphocyte population. This finding suggests that in the process of lymphocyte depletion more CD4-positive lymphocytes than CD8-positive lymphocytes are lost, and this might account for the impairment of cell-mediated immunity in Hodgkin's disease.     

Exposure of cynomolgus monkey embryos to retinoic acid causes thymic defects: effects on peripheral lymphoid organ development

We have previously reported that exposure of monkey embryos to 13-cis-retinoic acid (cRA) results in thymic defects. In this study, we analyzed lymphocyte and antigen-presenting cell populations at gestational days (GDs) 80-100 in the thymus, spleen, mesenteric lymph nodes, and gut-associated lymphoid tissue following a teratogenic dosing regimen of cRA (2.5 and 5 mg/kg) at GD14-27. Tissue sections were immunostained for T-cells (anti-CD3), B-cells (anti-CD20), dendritic cells (p55), and major histocompatibility class II (anti-HLA-DR). Digital images of spleen sections were analyzed to obtain the relative area occupied by the cell subsets within the white pulp (WP). Compared with controls, the T-cell dependent compartment of the spleen WP in specimens with perturbed thymic development (aplasia and severe hypoplasia) showed a reduction in size and proportion of CD3(+) T cells. Our findings indicate that cRA-induced thymic defects result in disrupted development of the splenic T-cell dependent compartment.     

Distribution of Lyt antigens on the surface of thymocytes associated with thymic macrophages and dendritic cells

Summary Thymocyte subpopulations that are associated with macrophages and dendritic cells of the thymus in vivo were isolated from the thymuses of C57Bl/6 mice, and their Lyt phenotypes were analyzed. Electron-microscopic examination of immunogold-labeled cells revealed that the thymic complexes formed by macrophages mainly contained Lyt-2-positive thymocytes, while Lyt-1-positive thymocytes were more frequently associated with dendritic cells. The characteristic distributions of Lyt antigens on the surface of thymocytes in regions of reciprocal contact with macrophages (Lyt-2-positive cells) and dendritic cells (Lyt-1-positive cells) suggest that these antigens play a role in specific interactions between thymocytes and stroma cells.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthday     

Differential recruitment of T- and IgA B-lymphocytes in the developing mammary gland in relation to homing receptors and vascular addressins.

The mammary gland (MG) develops new vasculature and is colonized by lymphocytes, primarily T-cells, during pregnancy. In contrast, during lactation it is colonized primarily by IgA-containing B-cells (c-IgA cells). To explain this difference, we analyzed the spatiotemporal relationships between lymphocytes that expressed peripheral or mucosal homing receptors (HR) and the location of their vascular counterreceptors using quantitative immunohistochemical techniques. We observed that the density of beta(7+)/CD3(+) T-cells varied with the amount of the mucosal addressin cell adhesion molecule-1 (MAdCAM-1)-stained area. Both increased during pregnancy to peak at delivery, decreased rapidly in early lactation to a steady level in mid- and late lactation, and returned to resting values after weaning. Although 60% of these beta(7+)/CD3(+) T-cells scattered in the epithelium co-expressed alpha(E)beta(7), whereas the remaining 40% in association with blood vessels were alpha(4)beta(7), these results are consistent with a role of MAdCAM-1 in the localization of alpha(4)beta(7+) T-cells. In contrast to T-cells, beta(7+)/c-IgA(+) B plasmablasts (approximately 30% of total c-IgA cells) were located at the alveolar confluence, and their numbers increased in mid- and late lactation when MAdCAM-1 density plateaued. However, both T-and B-cells decreased after weaning. These results show an association between MAdCAM-1 expression level and recruitment of T-cells that does not hold for c-IgA B cells. Furthermore, the recruitment and accumulation of alpha(4)beta(7+) c-IgA cells are reminiscent of locally produced chemoattractants. (J Histochem Cytochem 47:1581-1592, 1999)