Paracortical Areas Research Articles

Eosinophils function as antigen-presenting cells.

Eosinophils release lipid mediators, including leukotriene C4, platelet-activating factor, and liposins, and contain four distinct granule cationic proteins, major basic protein, eosinophil peroxidase, eosinophil cationic protein, and eosinophil-derived neurotoxin, which may cause dysfunction and destruction of other cells. Eosinophils are primarily thought of as terminal effectors of allergic responses and of parasite elimination. Eosinophils are characteristically present within the airway lumina of asthmatics, and these airway eosinophils have been induced in vivo to express major histocompatibility complex II (MHC-II) complexes and costimulatory molecules, which are required for T lymphocytes to be functionally activated. In in vitro experiments, eosinophils can process antigen and express the costimulatory molecules, and after cytokine-elicited induction of MHC-II, expression can function as antigen-presenting cells in stimulating T lymphocyte responses. Airway luminal eosinophils can migrate into draining paratracheal lymph nodes, localized to T cell-rich paracortical areas, and stimulate antigen-specific T cell proliferation in vivo within paratracheal lymph nodes, which was CD80- and CD86-dependent and limited to CD4+ T cells. Furthermore, eosinophils within the lumina of airways promote expansion of T helper cell type 2 (Th2) by presenting antigen, suggesting that eosinophils actively modulate immune responses by amplifying Th2 cell responses.

Dynamic Populations of Dendritic Cell-Specific ICAM-3 Grabbing Nonintegrin-Positive Immature Dendritic Cells and Liver/Lymph Node-Specific ICAM-3 Grabbing Nonintegrin-Positive Endothelial Cells in the Outer Zones of the Paracortex of Human Lymph Nodes

In the paracortex of lymph nodes, cellular immune responses are generated against antigens captured in peripheral tissues by dendritic cells (DCs). DC-SIGN (dendritic cell-specific ICAM-3 grabbing nonintegrin), a C-type lectin exclusively expressed by DCs, functions as an antigen receptor as well as an adhesion receptor. A functional homologue of DC-SIGN, L-SIGN (liver/lymph node-SIGN, also called DC-SIGN-related), is expressed by liver sinus endothelial cells. In lymph nodes, both DC-SIGN and L-SIGN are expressed. In this study, we analyzed the distribution of these two SIGN molecules in detail in both normal and immunoreactive lymph nodes. DC-SIGN is expressed by mature DCs in paracortical areas and in addition by DCs with an immature phenotype in the outer zones of the paracortex. L-SIGN expression was also detected in the outer zones on sinus endothelial cells characterized by their expression of the lymphatic endothelial markers LYVE-1 and CLEVER-1. During both cellular and humoral immune responses changes in the amount of DC-SIGN+ immature and mature DCs and L-SIGN+ endothelial cells were observed, indicating that the influx or proliferation of these cells is dynamically regulated.

Dynamics of mast cells in lymph node following antigenic stimulation.

Dynamics of mast cells in rat cervical lymph nodes were examined using conventional histological techniques after injection of Salmonella paratyphi B-H antigen. There was no significant change in the number of mast cells at sixth hour and on the first day of stimulation compared with the controls. The number of mast cells was increased in all lymph node compartments on the second day of stimulation, which continued in the following 3 days. On the eighth day of stimulation, although the mast cell number decreased in the subcapsular area, it was still high in the paracortical area and medullary sinuses of the lymph nodes. On the second day of stimulation, the mast cell number was apparently increased in the subcapsular area than those of the other compartments. In the following days of stimulation, the highest number of mast cells was seen in the medullary sinuses. The highest paracortical mast cell number was determined on the third day of stimulation and some mast cells were observed near the high endothelial venules (HEVs). The changes of mast cell number among the lymph node compartments after antigenic stimulation support the hypothesis that the migration of mast cells occurred. This migration pattern indicates that mast cells enter the lymph node via afferent lymphatics and migrate to the lymph node compartments following antigenic stimulation.

Immunoperoxidase studies of cell mediated immune effector cell populations in early Mycobacterium avium subsp. paratuberculosis infection in sheep.

Immunoperoxidase (IPX) labelling for CD4, CD8, TCR-gammadelta, WC1, CD1b, IFN-gamma, CD45R, CD56 and lysozyme was used to investigate changes in cell mediated immune effector cell populations in the intestinal Peyer's patches (PP) and mesenteric lymph nodes of lambs, 2 and 4 months after experimental infection with low doses of sheep strain Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis). The organism was cultured from the tissues of each infected lamb, but histological lesions were not present. This infection model was considered to be more representative of natural M. a. paratuberculosis infection than previous studies. Infected sheep had significantly more CD4+ cells in the mucosa, domes and interfollicular areas of the terminal ileum, and in the interfollicular areas of the jejunal Peyer's patch. Infected sheep also had significantly increased numbers of TCR-gammadelta+ cells in the mucosa and interfollicular areas of the jejunal Peyer's patch, and increased numbers of WC1+ cells in the ileal Peyer's patch. These findings are consistent with previous findings in sheep given higher doses of cattle strain M. a. paratuberculosis. Significantly fewer CD1b+ cells were present in the paracortical areas of the mesenteric lymph nodes of infected sheep, and the reduction was greater in sheep infected for 4 months compared to sheep infected for only 2 months. Down-regulation of CD1b expression may be important for the continued survival and multiplication of M. a. paratuberculosis as specific adaptive immunity develops. Across all sheep, jejunal Peyer's patches had higher numbers of CD4+, CD8+, TCR-gammadelta+, WC1+ and CD45R+ cells, and lower numbers of CD56+ fibres compared to ileal Peyer's patches. These findings confirm and extend the peculiarities of the terminal ileal Peyer's patch in the young ruminant, with possible implications for the early establishment of M. a. paratuberculosis infection.

Linear acral pseudolymphomatous angiokeratoma of children (APACHE): Further evidence that APACHE is a cutaneous pseudolymphoma

Acral pseudolymphomatous angiokeratoma of children (APACHE) is a recently recognized, rare clinical entity. We report a case of APACHE in a 9-year-old Japanese girl with a dark red, linear plaque on the posterior area of the right lower leg. Histopathologic findings revealed further evidence that APACHE was a cutaneous pseudolymphoma rather than a vascular neoplasm because of the presence of distinct primary and secondary lymphoid follicles, and thick-walled, long blood vessels lined with prominent plump endothelial cells similar to high endothelial venules in the paracortical area of the lymph node. In addition to previous descriptions, the patient presented with a distinct linear lesion. Vacuolar alteration of the basal cell layer and scattered eosinophilic bodies in the epidermis were observed, which suggested a lichenoid tissue reaction. We believe that APACHE might show a distinct linear pattern accompanied by a lichenoid tissue reaction. (J Am Acad Dermatol 2003;48:S15-7.)

The gut-associated lymphoid tissues of the northern brown bandicoot ( Isoodon macrourus)

The gut associated lymphoid tissues (GALT) of a juvenile bandicoot has been examined using histological and immunohistochemical techniques. The mesenteric lymph nodes were hyperfollicular and had well defined paracortical and medullary areas. Lymphocytes were densely packed throughout the cortex and paracortex and the mantles of the follicles. The GALT contained two distinct areas of tissue organisation. One consisted of large areas of aggregated follicles, whilst the other consisted of more linearly distributed follicles. The distribution of T and B cells in the tissue beds was documented using antibodies to surface markers CD3, CD5 and CD79b. T-cells were present in high numbers in the cortical region of the lymph node, whilst B-cells were predominant in the mantle of the follicles. Dispersed CD3 positive T-cells were abundant in the villi lacteals and present in high numbers in follicular areas of gut. CD79b positive B-cells were not observed in the lacteals but were abundant in the mantles of follicles. This is similar to that observed in other metatherians.

HSP70 is selectively over-expressed in the blast cells of the germinal centres and paracortex in reactive lymph nodes.

We evaluated by immunohistochemistry HSP70 expression in reactive lymph nodes since its morphological expression and location have not been previously described and correlated with lymphocyte kinetics. Ninety-six cases of non-specific lymphadenitis were immunostained for HSP70, CD20, CD3, Ki67, Bcl-2, CD21. The type and the location of HSP70-positive cells were determined. Their number out of 2000 cells in each germinal centre and in each paracortical area was counted at 60x magnification with the help of a quantitative grid. Seventeen percent of germinal centre cells and 7.6% of the paracortex cells were positive. This difference was highly significant. The positively reacting cells were B-cells and had a blast (centroblast or immunoblast) morphology, with negative mantle and marginal lymphocytes and T-cells. Lymphoplasmacytoid cells and plasma cells reacted only weakly or were negative. Germinal centre antigen-presenting cells and interdigitating dendritic cells reacted from lightly to moderately. HSP70 was selectively over-expressed by B-blasts mainly located within germinal centres with a lower number in the paracortex. The difference in the mean number between the two sites was statistically highly significant. No correlation was found with bcl-2 and Ki67 expression. Mantle, marginal and T-lymphocytes were always negative. The biological meaning and role of this over-expression in centroblasts and immunoblasts remain to be elucidated.

Angioimmunoblastic T-cell lymphoma with hyperplastic germinal centers: a clinicopathological and immunohistochemical study of 10 cases.

An absence of germinal centers is one of the histological characteristics of angioimmunoblastic T-cell lymphoma (AITL). We report here 10 unusual cases of AITL with hyperplastic germinal centers. The clinical presentation of each patient was characterized by generalized lymphadenopathy, constitutional symptoms and polyclonal hypergammaglobulinemia. The initial biopsy findings of each patient were similar and were characterized by hyperplastic germinal centers with ill-defined borders and a proliferation of high endothelial venules (HEV). In the paracortical area there was a mixed infiltrate including irregularly shaped clusters or small nests of clear cells in all cases. Moreover, the clear cells invaded the lymphoid follicles, resulting in expansion of the germinal centers, except for one case. Immunohistochemistry revealed that the tumor cells, including clear cells, were CD4-expressing T cells. Some of the atypical lymphocytes were also Bcl-6-positive. A majority of the follicular dendritic cell networks showed a normal/reactive or an expanded/disrupted pattern in all cases. Moreover, three lesions possessed a few large irregularly shaped proliferations of follicular dendritic cells around the HEV Four cases progressed to AITL within a few years. The present 10 cases probably represent an early stage of AITL preceding follicular dendritic cell hyperplasia. Detection of clear cells, Bcl-6-positive atypical T lymphocytes, and foci of irregularly shaped proliferation of follicular dendritic cells appears to be critical for early diagnosis and treatment of AITL with hyperplastic follicles.

Sentinel Lymph Nodes Show Profound Downregulation of Antigen-Presenting Cells of the Paracortex: Implications for Tumor Biology and Treatment

The sentinel lymph node (SN) is the first node on the direct lymphatic drainage pathway from a tumor. Melanoma-associated SNs are the most likely site of early metastases and their immune functions are strikingly down-modulated. We evaluated histologic and cytologic characteristics of 21 SNs and 21 nonsentinel nodes (NSNs) from melanoma patients who had clinically localized (AJCC Stage I–II) primary cutaneous melanoma. SNs showed highly significant reductions in total paracortical area and in the area of the paracortical subsector occupied by dendritic cells. The frequency of paracortical interdigitating dendritic cells (IDCs) was dramatically reduced in SNs, and most IDCs (∼99%) lacked the complex dendrites associated with active antigen presentation. The release of immunosuppressive factors from the primary melanoma may induce a localized and specific paralysis in the SN, which prevents the recognition of otherwise immunogenic melanoma antigens by IDCs. This immune paralysis may facilitate the implantation and growth of melanoma cells in the SN. Cytokine therapy may be able to reverse this immune paralysis. These findings have an important practical application in the histopathologic confirmation that a node is truly sentinel. They also offer an hypothesis to explain the failure of the immune surveillance mechanisms to identify and respond to a small primary melanoma that expresses immunogenic tumor antigens.

A description of parasite-harbouring cells in localized lymphadenitis in dry type cutaneous leishmaniasis

Lymphadenitis with or without dry-type cutaneous leishmaniasis is rare. The lesion might self heal or show excellent response to antimonial therapy. Routine histopathological changes of localized leishmaniasis lymphadenitis are non-caseating to suppurative granulomata mostly in paracortical areas, some with extension to germinal centres, medullary cords and/or pericapsular spaces which have to be distinguished from other causes of lymphadenitis such as tuberculosis, cat-scratch disease and toxoplasmosis. Dense lymphoplasmocytic infiltrate was observed surrounding the necrotizing granuloma together with dense capsular fibrosis with multiple granulomata in subcapsular and pericapsular areas. Immunostaining of lymph nodes showed that a few macrophages were harbouring Leishman bodies. Dispersed Langerhans cells were also harbouring Leishman bodies in the parasitophorous vacuoles between their cytoplasmic pseudopods. In conclusion multiple noncaseating to suppurative granulomata with dense pericapsular and capsular granulomo-sclerotic changes should be considered in the differential diagnosis of leishmaniasis lymphadenitis.

Dendritic cells are early cellular targets of Listeria monocytogenes after intestinal delivery and are involved in bacterial spread in the host.

We studied the sequence of cellular events leading to the dissemination of Listeria monocytogenes from the gut to draining mesenteric lymph nodes (MLNs) by confocal microscopy of immunostained tissue sections from a rat ligated ileal loop system. OX-62-positive cells beneath the epithelial lining of Peyer's patches (PPs) were the first Listeria targets identified after intestinal inoculation. These cells had other features typical of dendritic cells (DCs): they were large, pleiomorphic and major histocompatibility complex class II(hi). Listeria were detected by microscopy in draining MLNs as early as 6 h after inoculation. Some 80-90% of bacteria were located in the deep paracortical regions, and 100% of the bacteria were present in OX-62-positive cells. Most infected cells contained more than five bacteria each, suggesting that they had arrived already loaded with bacteria. At later stages, the bacteria in these areas were mostly present in ED1-positive mononuclear phagocytes. These cells were also infected by an actA mutant defective in cell-to-cell spreading. This suggests that Listeria are transported by DCs from PPs to the deep paracortical regions of draining MLNs and are then transmitted to other cell populations by mechanisms independent of ActA. Another pathway of dissemination to MLNs was identified, probably involving free Listeria and leading to the infection of ED3-positive mononuclear phagocytes in the subcapsular sinus and adjacent paracortical areas. This study provides evidence that DCs are major cellular targets of L. monocytogenes in PPs and that DCs may be involved in the early dissemination of this pathogen. DCs were not sites of active bacterial replication, making these cells ideal vectors of infection.

Autoimmune disease-associated lymphadenopathy with histological appearance of T-zone dysplasia with hyperplastic follicles. A clinicopathological analysis of nine cases.

Autoimmune disease-associated lymphadenopathy shows marked histopathological and clinical diversity. We describe the clinicopathological and immunohistochemical findings of nine cases of autoimmune disease-associated lymphadenopathy, which posed a serious differential diagnostic problem regarding T-zone dysplasia with hyperplastic follicles. There were two males and seven females aged 25 to 65 years (median 37 years). The patients had multicentric lymphadenopathy in association with clinical and laboratory findings suggestive of an "autoimmune disease". Four patients were diagnosed to have systemic lupus erythematosus (SLE), and the remaining five patients had antiphospholipid antibody syndrome and Sjogren's syndrome (SS), rheumatoid arthritis (RA), chronic thyroiditis, RA and SS, and SLE and SS, respectively. None of the nine patients developed malignant lymphomas during the follow-up periods from 44 to 225 months (median 103 months). The lesions were characterized by paracortical hyperplasia with prominent vascular proliferation and many lymphoid follicles with germinal centers. The paracortical area usually contained numerous small T-lymphocytes without cytological atypia, accompanied by a variable number of plasma cells, B-immunoblasts, and histiocytes. Polymerase chain reaction analysis demonstrated no clonal rearrangement of the T-cell receptor chain gene in four cases examined, although immunoglobulin heavy chain rearrangement was detected in only one case. These findings suggest that autoimmune disease-associated lymphadenopathy, especially SLE, shares the histological features with T-zone dysplasia with hyperplastic follicles. The nine cases presented here should be differentiated from T-zone lymphoma with follicles and angioimmunoblastic lymphoma with hyperplastic germinal centers. To avoid overdiagnosis and overtreatment, we emphasize the need to turn attention to these clinical and laboratory findings as well as to the morphological features.

Ｅｐｓｔｅｉｎ‐Ｂａｒｒ ｖｉｒｕｓの感染を伴った組織球性壊死性リンパ節炎（菊池病）の１例

A case of histiocytic necrotizing lymphadenitis (Kikuchi's disease) accompanied by elevation of the serum antibody against Epstein-Barr virus (EBV)-viral capsid antigen is presented. On histopathological and immunohistochemical studies, infiltration of numerous macrophages (CD68+) and T cells (CD45RO+) was seen around the periphery of a necrotic lesion in the paracortical area of lymph nodes, showing a reduced CD 4+/CD 8+ratio. Furthermore, EBV-encoded latent membrane protein (LMP-1) was detected in the lymphocytes of involved lymph nodes. These findings suggest that this case might be related to EBV infection.

Selective Modulation of Paracortical Dendritic Cells and T-Lymphocytes in Breast Cancer Sentinel Lymph Nodes.

Sentinel nodes (SNs), the nodes nearest a primary tumor on the direct lymphatic drainage path, are the site of earliest metastases, and in melanoma show striking immune modulation. We evaluated SNs from breast cancer patients for evidence of similar immune perturbation. The purpose of this study was to evaluate whether SNs from patients with breast cancer show the alterations in the histology and cytology of the paracortical areas seen in SNs from patients with melanoma. Formalin-fixed and paraffin-embedded sections from 32 SNs and 32 nonsentinel nodes (NSNs) from patients with breast cancer were evaluated. Sections were stained with hematoxylin and eosin and with antibodies to S-100 protein and HLA-DR, DQ, and DP to identify interdigitating dendritic cells (IDCs), and by an antibody to CD43RA to delineate T lymphocytes. By computerized image analysis we evaluated the distribution, frequency, immunophenotype, and activation status of IDCs and associated T lymphocytes in SNs and NSNs. Average areas occupied by S-100-positive dendritic cells (DCs) in SNs and NSNs were 0.13% and 19.98%, respectively, of total nodal area (p < 0.0001). The average density of S-100-positive IDCs in SNs was 11.00/mm2 and in NSNs was 257.88/mm2 (p < 0.0001). In SNs 43.55% of DCs (4.93/mm2) were nondendritic, 51.92% (5.69/mm2) had short dendrites, and 5.2% were mature with long dendrites (0.62/mm2). In SNs the ratio of immature to mature IDCs was 7.95:1. In NSNs, 8.09% of DCs (8.5/mm2) were nondendritic, 28.22% (67.46/mm2) had short dendrites, and 63.07% (145.96/mm2) were mature DCs with long dendrites. The ratio of immature to mature DCs in NSNs was 1:6.66. The average areas occupied by HLA class II-positive DCs in SNs and NSNs were 4.21% and 31.82%, respectively, of total nodal area. The frequency of coexpression of S-100 and HLA class II by immature IDCs without dendrites was 11.27% in SNs and 15.00% in NSNs. In both SNs and NSNs (p < 0.001) all mature S-100-positive IDCs with long dendrites expressed HLA class II. CD43RA-positive T lymphocytes occupied 20.06% of total nodal area in SNs and 63.57% in NSNs (p < 0.0001). The SNs from breast cancer patients are profoundly immune modulated with, by comparison to NSNs, markedly reduced paracortical areas, densities of paracortical DCs, frequency of S-100-positive IDCs coexpressing HLA class II, and a predominance of immature nondendritic and poorly dendritic DCs.

Anaplastic large-cell lymphoma associated with acquired ichthyosis

Anaplastic, CD30+, large-cell lymphoma (ALCL) is a subtype of non-Hodgkin’s lymphoma that accounts for 2% to 8% of all lymphomas. Its most common form is a classical systemic type, which involves multiple nodal and extranodal sites, including the skin. Malignant lymphoproliferative disorders, especially Hodgkin’s disease, are known rarely to be associated with acquired ichthyosis, whereas only 1 case of ALCL has been reported to be associated with acquired ichthyosis. We describe a 74-year-old Japanese man with ALCL, involving lymph nodes and the skin, who exhibited acquired ichthyosis. The clinical and histopathologic findings were recorded, and immunophenotyping, T-cell receptor (TCR), and immunoglobulin gene rearrangement were determined. Clinically, right axillary and bilateral inguinal lymph nodes were palpable. The cutaneous eruptions were multiple pinkish and yellow colored, up to thumb-sized nodules, some of which were ulcerated. Histologically, the right axillary lymph node showed proliferation of anaplastic large cells in the paracortical and sinusoidal areas. Both the lymph node and skin showed pleomorphic proliferation of lymphoid cells with a mixture of mononuclear cells having oval, embryo-shaped, reniform, and lobulated nuclei, binucleated Reed-Sternberg–like cells, and multinucleated cells, with giant anaplastic and wreath-shaped nuclei. Immunophenotyping of the neoplastic cells revealed that they were positive for CD30 (Ber-H2), CD15 (Leu-M1), CD45 (LCA), and CD45RO (UCHL-1). Southern blot analysis demonstrated clonal rearrangement of the TCR β region. In contrast, no novel bands were detected with the immunoglobulin heavy chain JH probe. Several months after the detection of the axillary nodes, an ichthyosiform, scaly eruption developed over almost the entire body of the patient. Histologically, it showed orthokeratotic, slight hyperkeratosis of the epidermis without a granular layer or with only a single layer of cells in the granular layer. Several kinds of lymphoproliferative diseases are associated with acquired ichthyosis, including Hodgkin’s disease, multiple myeloma, and lymphomatoid papulosis. This is the second case report of acquired ichthyosis associated with ALCL. Although a common pathomechanism is suspected of underlying the development of acquired ichthyosis in these diseases, it is still unexplained. (J Am Acad Dermatol 2000;42:914-20.)

Cellular immune response of lymph nodes from dogs following the intradermal injection of a recombinant antigen corresponding to a 66 kDa protein of Echinococcus granulosus

A recombinant polypeptide (referred to as EgA31), which represents a 66 kDa protein, was prepared from an Echinococcus granulosus cDNA library. In order to assess its potential to induce cellular immune responses, dog popliteal and prescapular lymph nodes were sensitized with this recombinant polypeptide. Subpopulations of lymphocytes were then analyzed by flow cytometry and immunohistochemistry on lymph node sections. Five days after the sensitization, the paracortical areas of the lymph nodes appeared hypertrophic, the number of CD3+, CD4+, CD8+ and CD5+ cells increased, the number of B-cells began to augment and some secondary follicles occurred, and a number of CD4+ cells appeared in germinal centers. Many large secondary follicles and a significantly augmented number of CD5+ cells in cords of medullae were observed 10 days after the sensitization. These active cellular responses strengthen the interest for further studies on the development of a vaccine with this recombinant polypeptide.

Lymph node trafficking and antigen presentation by endobronchial eosinophils.

Because eosinophils recruited into the airways in allergic diseases are exposed to inhaled allergens, we evaluated whether eosinophils within the endobronchial lumen can function in vivo as antigen-presenting cells for inhaled antigens. We recovered eosinophils from the airways after aerosol antigen challenge in sensitized mice or from the peritoneal cavities of IL-5 transgenic mice and fluorescently labeled these cells ex vivo. These labeled cells, instilled intratracheally into normal mice, migrated into draining paratracheal lymph nodes and localized to T cell-rich paracortical areas. The homing of airway eosinophils to lymph nodes was not governed by eotaxin, because CCR3(-/-) and CCR3(+/+) eosinophils migrated identically. Airway eosinophils, recovered after inhalational antigen challenge in sensitized mice, expressed MHC class II and costimulatory CD80 and CD86 proteins and functioned in vitro as CD80- and CD86-dependent, antigen-specific, antigen-presenting cells. Moreover, when instilled into the airways of antigen-sensitized recipient mice, airway eosinophils recovered after inhalational antigen challenge stimulated antigen-specific CD4(+) T cell proliferation within paratracheal lymph nodes. Thus, eosinophils within the lumina of airways can process inhaled antigens, traffic to regional lymph nodes, and function in vivo as antigen-presenting cells to stimulate responses of CD4(+) T cells.

Antigen-presenting cells in nasal allergy.

Antigen-presenting cells in nasal allergy.

Accumulation of MAC387 + macrophages in paracortical areas of lymph nodes in rhesus monkeys acutely infected with simian immunodeficiency virus

We investigated the histological features of lymph nodes, focusing on monocytes/macrophages, in rhesus monkeys ( Macaca mulatta) acutely infected with simian immunodeficiency virus (SIV). In monkeys infected with a pathogenic SIV, SIVmac239, MAC387 + newly blood-derived macrophages markedly increased in number at paracortical areas at 11 to 14 days postinoculation, concomitant with the peak of the primary SIV antigenemia. The MAC387 + macrophages densely gathered around high endothelial venules and formed cell clusters with CD3 + T lymphocytes, tingible body macrophages, and plasmacytoid monocytes. In the cell clusters, CD3 + T lymphocytes which closely adhered to the MAC387 + macrophages enlarged in size, suggesting a histological manifestation of T-lymphocyte activation by macrophages. By 54 days postinoculation, when SIV antigenemia became undetectable, the MAC387 + macrophages decreased in number and the cell cluster disappeared from paracortical areas. In contrast, the monkeys infected with a nef-deleted mutant of SIVmac239 showed lower levels of SIV antigenemia and lower numbers of MAC387 + macrophages in paracortical areas than those infected with SIVmac239. These results indicate that MAC387 + macrophages accumulate in paracortical areas for the period of the intense primary SIV antigenemia and may play an important role in activating naive T lymphocytes.

Expression of the RelB transcription factor correlates with the activation of human dendritic cells.

The RelB gene product is a member of the nuclear factor (NF)-kappaB family of transcription factors. It has been identified recently within mouse antigen-presenting cells and human monocyte-derived dendritic cells (DC). Disruption of the mouse RelB gene is accompanied, amongst other phenotypes, by abnormalities in the antigen-presenting cell lineages. In order to define RelB expression during human DC differentiation, we have analysed RelB mRNA by reverse transcriptase-polymerase chain reaction and RelB protein by intracellular staining in CD34+ precursors and different types of DC preparations. RelB mRNA was not detected in CD34+ precursor populations. Fresh blood DC (lineage-human leucocyte antigen-DR+ (lin-HLA-DR+)) lacked RelB mRNA and cytoplasmic RelB protein but a period of in vitro culture induced RelB expression in blood DC. Purified Langerhans' cells (LC) (CD1a+ HLA-DR+) failed to express RelB mRNA. Immunocytochemical staining identified RelB protein in human skin epithelium. RelB protein was expressed in a very few CD1a+, CD83+ or CMRF-44+ dermal DC but was not present in CD1a+ LC. Tonsil DC (lin-HLA-DR+ CMRF-44+) were positive for RelB mRNA and RelB protein. Intestinal DC (HLA-DR+) also lacked immunoreactive RelB protein. The majority of interdigitating CD83+, CMRF-44+, CMRF-56+ or p55+ DC located in paracortical T-lymphocyte areas of lymph node and tonsil contained RelB protein. The expression of RelB mRNA and RelB protein correlates with the activated phase of blood DC and the postmigration cell (activated) stage of tissue DC development.