Studies of Ia antigens on murine peritoneal macrophages

HLA-D-associated 'Ia-like' antigens on human macrophages

Human macrophages procured by culture of adherent peripheral blood mononuclear cells were investigated for reactivity in complement-dependent cytotoxicity tests with antisera having specificity for HLA-D-associated 'Ia-like' B-cell antigens. The antisera were found to be cytotoxic for 30%-70% of the macrophages from donors whose B cells were also reactive, and absorption with B cells also removed macrophage cytotoxicity. A B-cell xenoantiserum was also cytotoxic to macrophages. It is concluded that the HLA-D-associated 'Ia-like' antigens present on B cells are also expressed by macrophages, at least on a subpopulation.

Expression of MHC class II antigens on rat bone marrow cells and macrophages, and their modulation during culture with murine GM-CSF or M-CSF

Flow cytometric analysis employing MRC OX 6 and MRC OX17 monoclonal antibodies recognizing determinants on RT1.B or RT1.D molecules, equivalent to murine I-A and I-E, respectively, was used to detect rat MHC class II antigen (Ag) expression. Approximately 5% of freshly isolated rat bone marrow cells (BMC) expressed RT1.B and over 30% displayed RT1.D molecules. The RT1.D+ cells were W3/13+, OX 7+, OX 19- and OX 22-. After one week culture of BMC with murine recombinant granulocyte/macrophage colony-stimulating factor (GM-CSF), regardless of concentrations, 90 to 95% of the cells were scored as bone marrow-derived macrophages (BMDM phi), and over 30% expressed both RT1.B and RT1.D Ag. GM-CSF increases the percentage of BMDM phi bearing MHC class II Ag in a concentration-dependent manner. This effect seems to be specific because antibodies to interferon-gamma, tumor necrosis factor-alpha or interleukin-4 did not reduce the number of cells expressing RT1.B and RT1.D Ag. Furthermore, GM-CSF was able to trigger expression of class II molecules on rat peritoneal macrophages (M phi) and BMDM phi resulted from cultures of BMC with mouse M phi-CSF (M-CSF), and the RT1.B and RT1.D inducing effect of GM-CSF was opposed by M-CSF, and by anti-GM-CSF antibodies. The induction of MHC class II Ag synthesis by GM-CSF on rat BMDM phi was confirmed at the mRNA level by Northern blot analysis employing cDNA probes encoding the RT1.B alpha.

Evaluation of murine splenic cell type metabolism of benzo[a]pyrene and functionality in vitro following repeated in vivo exposure to benzo[a]pyrene

Recent studies have demonstrated that macrophages are the cell types capable of metabolizing benzo[a]pyrene (B(a)P) within the spleens of untreated mice. Since repeated exposure to B(a)P results in immunosuppression and B(a)P is known to induce cytochrome P450 levels, the first objective of this study was to investigate whether exposure of mice to B(a)P could increase the amounts of immunosuppressive B(a)P metabolites generated and/or alter the pattern of B(a)P metabolites formed by several different splenic cell types. Mice were dosed with a daily sc dose of 200 mg/kg B(a)P or vehicle for 4 days. Separation of splenocytes based on density by centrifugation through discontinuous Percoll gradients along with immunomagnetic negative selection or antibody-mediated complement lysis was used to obtain different splenic cell populations. Cells were incubated with [3H]B(a)P for 24 hr. High-pressure liquid chromatography was used to separate and quantitate B(a)P metabolites. Results indicate that splenic macrophages of B(a)P-treated mice produced significantly greater amounts of some metabolites compared to those of vehicle-treated mice. The three major metabolites produced were an unidentified peak of polar metabolites containing polyhydroxylated metabolites, B(a)P-9,10- and B(a)P-7,8-dihydrodiols. Other splenic cell types examined did not produce metabolite amounts significantly above (T-cells, PMNs, or the capsule) or just above (B-cells) background. The second objective was to investigate the splenic cell type(s) targeted by B(a)P resulting in suppression of humoral immunity. Separation-reconstitution studies along with in vitro sensitization techniques with several different antigens (sheep red blood cells (SRBC), dinitrophenyl-Ficoll (DNP-Ficoll), lipopolysaccharide (LPS)) were used to identify splenic target cells following exposure of mice to B(a)P (200 mg/kg/day, sc for 4 days). Findings indicate that in vitro plaque-forming cell (PFC) suppression was due to alterations in the adherent (macrophage) cell population. Exposure also suppressed the PFC response to the T-dependent antigen SRBC and the T-independent antigen DNP-Ficoll, but did not suppress the PFC response to the polyclonal antigen, LPS. These data suggest that B(a)P is targeting macrophages.

Thy-1 positive tingible body macrophages (TBM) in mouse lymph nodes

This study was prompted by the observation that cells in mouse lymph nodes (LN) with cytological characteristics of tingible body macrophages (TBM) appeared to be Thy-1 positive. The objective of this study was to determine if these large cells were TBM and to conclusively demonstrate their reactivity for Thy-1. The cells were studied using monoclonal antibodies (MoAb) against Thy-1 and macrophage markers including F4/80 and Ia antigens at both light microscopic (LM) and electron microscopic (EM) levels. Immunocytochemical reactivity by TBM for Thy-1 antigen specific MoAb was demonstrated by LM in both in situ and in vitro LN preparations. Furthermore, ultrastructural examination of these germinal center cells in situ demonstrated that the Thy-1 reactivity visualized at the LM level was associated with ribosomes and endoplasmic reticulum as well as their plasma membrane. Similarly, these cells expressed intracytoplasmic and membrane reactivity for Ia antigens and also for the macrophage specific antigen F4/80. This indicates that the reactivity is due to active synthesis of the Thy-1 antigen and not attributable to reactivity of any phagocytosed Thy-1 positive cells. As defined by their germinal center location and morphological characteristics, these Thy-1 reactive macrophages were identified as TBM. Germinal center TBM thus represent a unique, vigorously phagocytic subset of mature macrophages which express both macrophage and thymocyte markers.

Myelin phagocytosis in Wallerian degeneration. Properties of millipore diffusion chambers and immunohistochemical identification of cell populations

Myelin phagocytosis in Wallerian degeneration was studied using a model of murine sciatic nerve degeneration in millipore diffusion chambers in the peritoneal cavity of host mice. Immunocytological investigations showed the dependence of myelin digestion on the invasion of Fc-positive, Mac-1-positive and partly Ia-positive monocytes. Lymphocytes did not play a prominent role. Compared to Wallerian degeneration in situ, phagocytosis was decreased in nerves enclosed by millipore membranes on both sides of the chamber. The membrane acted as a trap for invading monocytes/macrophages. Neither tissue integrity nor genetic strain influenced the degree of phagocytosis. A modification of the experimental technique is introduced which permits myelin phagocytosis in the peritoneal cavity in a degree comparable to that in Wallerian degeneration in situ.

Age-associated changes in Langerhans cells of murine oral epithelium and epidermis

Oral mucosa and skin of older individuals are immunologically less responsive to a range of allergens, but it is not known whether this is due to changes in the number of Langerhans cells or to impaired cell function. EDTA-separated epithelial sheets from the cheek and palate mucosa, and from ear aN< footpad skin of three-month-old and 24-month-old C57BL/6NNia mice were stained for ATPase, beta-glucuronidase activity and Iab-surface antigen to demonstrate Langerhans cells. The general distribution of such cells was unchanged with age, but those in epithelia from the old mice were more varied in shape, with irregular celL bodies and more elongated dendritic processes. The numerical density of Langerhans cells in old mice was reduced by 30-59 per cent compared with that in young mice.

Antigenic phenotyping of isolated and in situ rodent follicular dendritic cells (FDC) with emphasis on the ultrastructural demonstration of Ia antigens

The antigenic phenotype of mouse lymph node follicular dendritic cells (FDCs) was studied by immunocytochemical techniques. Indirect fluorescence was used in conjunction with monoclonal antibodies to localize FDC surface antigens on FDC-enriched cell preparations and in cryostat sections. Lymph nodes from rats and mice were also labeled directly for Ia antigens with fluorescein- or peroxidase-conjugated Ia-specific monoclonal antibodies (i.e., MRC Ox4 and 10-2.16, respectively). Lymphoid tissue was also prepared for electron microscopy to allow clear distinction between Ia antigens of B lymphocytes and FDCs in situ. In these experiments, gold-labeled antigen was used to clearly identify FDCs and their processes among the Ia-positive cells of lymph node follicles. The labeling observed by light and electron microscopy showed that FDCs expressed Ia in situ and in vitro. Additional surface determinants shown to be expressed by FDCs included H2-K, common leukocyte antigen, and the receptor for the Fc portion of IgG1 and IgG2b. Neither macrophage antigens, such as Mac-1, Mac-2, Mac-3, and F4/80, nor the lymphocyte markers Ly-1, Ly-2, and Thy-1 were expressed by FDCs. Thus, the antigenic phenotype of FDCs, along with their distinctive dendritic morphology, their nonphagocytic and nonadherent nature, and their ability to trap and retain immune complexes on their plasma membrane, identifies them as a unique cell population.

Multiple mechanisms regulate the expression of murine immune response genes

The immune response antigens (la antigens) are heterodimeric cell-surface glycoproteins that regulate lymphocyte and macrophage interactions leading to the production of antibody against foreign antigens. The class II genes in the I region of the murine major histocompatibility complex encode the alpha and beta chains of the two known la antigens, I-A and I-E. Molecular cloning of the I region led to the discovery of three DNA regions, A beta 2, psi A beta 3, and E beta 2, which share some nucleotide homology with the classical class II beta genes. In this report we present evidence that A beta 2 is transcribed in spleen and in a cultured B cell hybridoma. A beta 2 mRNA is also found on membrane-bound polysomes, suggesting that it is translated. In contrast to the classical I region genes, A beta 2 transcripts are not induced in macrophage cells by gamma-interferon (gamma-IFN). This difference in sensitivity to gamma-IFN suggests that B cells and macrophages regulate the expression of the class II genes by distinct mechanisms.

Interactions of small B lymphocytes with unprimed noncytolytic T cells: dissociation between "presentation" and growth induction

The accessory cell requirements in lectin-dependent triggering and growth of unprimed Lyt-2-T lymphocytes were analyzed by quantitatively comparing the ability of small B cells and peritoneal macrophages to either induce reactivity to growth factors or support growth. Lightly or nonirradiated small B cells were 15 to 30-fold less efficient as compared to T cell-depleted peritoneal cell populations, in the support of the lectin-stimulated Lyt-2-T cell proliferation. In contrast, lightly irradiated small B lymphocytes were quantitatively as efficient as macrophages in mediating lectin-driven Lyt-2-T cell proliferation, if relevant supernatants were added into culture. Finally, supernatants derived from cultures where T-small B cell ratios were optimal for growth of responder Lyt-2-lymphocytes were two orders of magnitude less efficient than conditioned medium obtained from cultures containing optimal T-macrophage ratios, in their ability to support growth of activated T cells. We conclude from these experiments that: in contrast to cytolytic T cell precursors, lectin-dependent induction of unprimed Lyt-2- T lymphocytes requires accessory cells; small B cells and macrophages are equally competent in this respect; and growth support by small B cell populations is due to contamination by macrophages which are the only cell type performing this function. We therefore interpret reports on Lyt-2- T cell proliferation upon stimulation with high numbers of small B cells as a two-step process: "presentation" and induction of T cells which is essentially B cell dependent, and factor production ensured by contaminating macrophages.

HLA class I genes: from structure to expression, serology and function

HLA class I genes have been isolated from phage and cosmid libraries and assayed by transfection into murine L cells. The transfection step proved to be very important because of the large number of genes (and pseudogenes) in this family. All functional genes characterized so far in this way are "classical" class I genes, i.e. members of the HLA-A, -B or -C families. Three of these have been sequenced (HLA-A3, -Aw24; HLA-Cw3) in addition to the pHLA 12.4 pseudogene. Sequence comparisons indicate, in particular, extreme conservation of the 3' non-coding region between allelic HLA-A locus genes; the general organization of all these genes (8 exons) is very similar. Restriction mapping around the functional genes has been performed to investigate the degree of conservation (e.g. between HLA-A3 regions from 2 different individuals) and examine allelism at the DNA level (e.g. between HLA-A3 and HLA-Aw24 regions). Exon shuffling experiments followed by serological analysis of the expressed product indicate that, as expected, specificities are determined by the first two domains of the molecule. However, further constructs show that as soon as a single exon is exchanged most specific reactivities disappear. CTL analysis of murine cells expressing HLA molecules has run into many difficulties but still holds promise for the study of structure-function relationships in this system.

Ia determinants on macrophages

It is well established that T cells cannot be activated by antigen alone but only if antigen is presented in context with I region associated (Ia) determinants. As a matter of fact, antigen-presenting cells or accessory cells, which are obligatory for the induction of any type of immune response, all share the same major characteristic of Ia expression. Thus, there seems to be a direct correlation between accessory cell function and Ia expression. Originally, Ia determinants were only detected on a few cell types, B cells and macrophages being the first. However, during the course of time, more and more cells were found to be Ia positive (Ia +) and it is possible that most cells can express Ia, if appropriately induced. The regulation of Ia expression has been best studied in macrophages, where it has been found that positive induction elements include phagocytosis and gamma-interferon, while prostaglandin E and alpha-fetoprotein tend to down-regulate the expression of Ia. The regulation of Ia expression on accessory cells is thus an integrated part of immune regulation. It is highly likely, although not yet directly proven, that the Ia molecules are the products of the immune response (Ir) genes located within the major histocompatibility complex. They may even be the mediators of the Ir genes which determine whether an immune response can take place at all and/or the extent of the response. Recently, it has been shown that not all Ia + cells are able to activate every known T cell function.(ABSTRACT TRUNCATED AT 250 WORDS)

The Langerhans cell, as a representative of the accessory cell system, in health and disease

Cell surface receptors and antigens present on Langerhans' cells (LC) suggest a close relationship between LC and interdigitating cells (IDC) in lymph node sections or lymphoid dendritic cells (LDC) in cell suspensions. One of the reported differences is that Fc receptors (FcR) which are present on LC, are absent on LDC. This difference can at least partly be explained by a laboratory artefact: FcR on murine LC are irreversibly modulated by the Ig that contaminates the bovine albumin commonly used for gradients. Furthermore, the demonstration of FcR on murine LC requires prolonged exposure to EA at 4 degrees C. A significant percentage of nonadherent, low density, Ig- lymph node cells also express such FcR. These cells can stimulate syngeneic mixed lymphocyte reactions as can LC isolated from epidermis. Consideration of LC as cutaneous representatives of the accessory cell system led to an investigation of their numbers in epidermal sheets of patients with acquired immunodeficiency syndrome (AIDS). A marked reduction in Ia+, ATPase+, OKT6+ LC was found as compared to controls, suggesting that accessory cell deficiency may play a role in the extreme immunodeficiency seen in AIDS patients.

Soluble Mlsa antigens: stimulatory effect in vitro versus suppressive effect in vivo

Using a pair of congenic strains of mice differing only at the Mls haplotype (Mls locus and closely linked genes), BALB/c (Mlsb) and BALB.D2-Mlsa, we have compared the in vitro proliferative responses of Mlsb lymphocytes to Mlsa antigens presented on either lymph node cells (LNC) or peritoneal adherent cells (PAC). Results showed that Mlsa-PAC are stronger stimulators than Mlsa-LNC, and furthermore, that the supernatant from Mlsa-PAC may be effective in eliciting a lymphocyte proliferative response. The proliferation in response to PAC supernatant is partially due to activation by nonspecific factor(s); however, the response in the presence of Mlsa incompatible PAC supernatant is about three times greater than the response obtained in the presence of syngeneic Mlsb-PAC supernatant, suggesting an additional stimulation by soluble Mlsa antigens. Contrasting with the ability of PAC-supernatant to stimulate a primary proliferative response in vitro, the in vivo immunization of Mlsb mice with Mlsa-PAC supernatant abrogates the specific proliferative response in subsequent one-way mixed lymphocyte cultures. This abrogation of the specific response is comparable to that observed after immunization with intact Mlsa peritoneal or spleen cells, although in the latter case the anti-H-2 proliferative response is also decreased, regardless of whether the H-2 incompatible stimulating cells express an additional incompatibility for Mlsa. The proliferation of untreated, but not of Mlsa-immunized BALB/c LNC, is stronger in cultures with DBA/2 stimulating cells (incompatible for Mlsa and other non-H-2 antigens) than in cultures with BALB.D2-Mlsa cells (incompatible for Mlsa alone), and is comparable in intensity to that activated by H-2 incompatibility. We conclude that Mlsa antigens are more efficiently recognized by unprimed helper T cells when presented on PAC than when presented on LNC. In the primary proliferative response, the effects of Mlsa and other non-H-2 antigens may be cumulative. In vivo immunization against Mlsa antigens results in suppression of the specific proliferative response and, to a certain extent, of the nonspecific proliferative response (directed against both H-2 and other non-H-2 antigens). Since Mlsa antigens are obtainable in soluble form, their physico-chemical purification can now be envisaged.

Persistent expression of Ia-antigen on a subpopulation of murine resident peritoneal macrophages

The stability of Ia-antigen expression on murine resident peritoneal macrophages was assessed during the course of in vitro culture. Contrary to published findings with radioimmunoassays and immunofluorescence assays, the cultured cells bore Ia-antigen, as shown by their rosetting with sheep erythrocytes coupled with anti-Ia.2 monoclonal antibody. In support of this finding, cultured cells presented the copolymer of glutamine, alanine, and tyrosine (GAT) to GAT-primed T lymphocytes in an Ia-dependent manner. Thus, functional Ia antigen is present on cultured macrophages. Disappearance of the antigen after fixation of macrophages with either glutaraldehyde or paraformaldehyde, a routine procedure in the radioimmunoassays and immunofluorescence assays, explains its presumed absence on cultured cells.

Staining of Langerhans cells with monoclonal antibodies to macrophages and lymphoid cells

Langerhans cells are Ia-bearing antigen-presenting cells in the epidermis that share many functions with macrophages. We have used monoclonal antibodies to the macrophage antigens, Mac-2 and-3, Ia antigen, Fc fragment receptor and the common leukocyte antigen CLA to compare the cell surface antigens of these cells with those of interdigitating and follicular dendritic cells and of macrophages in lymphoid tissues. Immunoperoxidase staining was carried out with epidermal sheets from BALB/c mice and epidermal cell suspensions enriched for Langerhans cells by Fc rosetting. Langerhans cells stained for all of these antigens. Comparison with the staining properties of other dendritic cells and macrophages, in combination with previous observations, indicates a close relationship of Langerhans cells to the interdigitating cells of lymphoid tissues.

The suppressive effect of peritoneal exudate macrophages on production of antibody to sheep erythrocytes in vitro

The effects of peritoneal exudate macrophages on antibody response to sheep erythrocytes (SRBC) were investigated in mice. Peritoneal exudate macrophages obtained from mice injected intraperitoneally with proteose peptone or Corynebacterium parvum 4 days earlier had stronger ability to phagocytize and degrade SRBC than normal resident macrophages. These macrophages suppressed antibody formation to SRBC in vitro as well as in vivo. This suppression was overridden by increasing the amount of SRBC and diminished completely by pretreatment of the macrophages with iodoacetate and partly by pretreatment with 2-deoxyglucose, both known to be inhibitors of phagocytosis, but not by addition of indomethacin to the in vitro culture. These results suggest that the suppression of antibody response by peritoneal exudate macrophages was due to the increased activity of these cells as scavenger cells, resulting in a reduced amount of effective antigenic stimulation, and that it was not mediated by a prostaglandin-dependent mechanism. The scavenger function of these macrophages may be due to Ia-negative macrophages.

Cytofluorometric analysis of major histocompatibility antigens on human monocytes using monoclonal antibodies

The expression of HLA-A, B, C, and DR antigens was investigated on monocyte preparations by flow cytometry using various monoclonal antibodies. Essentially all human monocytes, either freshly isolated or after culture for several days, were stained for HLA-A, B, C, and DR antigens. When monocytes were incubated with Con-A-stimulated lymphocyte supernatants, an increase in HLA-A, B, C, and DR staining was observed. No increase was noted when two other monoclonal antibodies against non-HLA-related monocyte antigens (63D3 and 61D3) were studied under the same culture conditions. These results indicate that soluble factor(s) present in Con-A-stimulated lymphocyte supernatants modulate the expression of the major histocompatibility antigens on the surface of human monocytes.

Demonstration of histiocytes in the epidermal infiltrate of mycosis fungoides

The presence of histiocytes in the epidermal and dermal infiltrate of mycosis fungoides was observed histochemically by revealing a diffuse pattern of acid alpha-naphthyl acetate esterase (ANAE) activity in the cytoplasm, and immunohistochemically by demonstrating the presence of histiocyte-specific 'enzymes', lysozyme, alpha-I-antitrypsin and alpha-I-antichymotrypsin. Histiocytes in the infiltrate of mycosis fungoides may be involved in antigen processing and interaction with T lymphocytes.

Immunoelectron microscopic identification of Langerhans cells using a new antigenic marker

The specificity of a monoclonal antibody (OKT6) for epidermal Langerhans cells was examined by immunoelectron microscopy. Peroxidase-labeled OKT6 bound to 1-5% of suspended human epidermal cells, as determined by light microscopy. Electron microscopic examination of peroxidase-labeled cells revealed that all Birbeck granule-containing Langerhans cells bound OKT6. In addition, a small population of indeterminate cells, lacking the Birbeck granule, was also labeled with OKT6. The ultrastructural studies confirm the specificity of OKT6 for Langerhans cells and suggest that the indeterminate cell represents a related cell population.

Role of Ia antigens in graft vs. host reactions. II. Molecular and functional analysis of T cell alloreactivity by the characterization of host Ia antigens on alloactivated donor T cells

Graft vs. host response (GVHR)-activated donor T cells bind to stimulatory host cell-derived Ia antigens. Radioimmune cell-binding assays demonstrate that activated donor T cells acquire both host I-A and I-E alloantigens on their surface. Approximately threefold to fivefold less I-E products than I-A products are transferred. Immunoprecipitation and one-dimensional and two-dimensional gel electrophoresis analyses show that radioiodinated alpha and beta polypeptide chains of both I-A and I-E-encoded host Ia molecules may be transferred in an apparently structurally unaltered form from host cells to donor cells. Biosynthetic studies indicate that [35S]methionine-labeled activated donor T cells do not synthesize Ia antigens of the donor haplotype. Functional analyses with fluorescence-activated cell sorter sorted donor T cell subpopulations show that donor T cells that bind host I-A antigens preferentially cooperate with nonimmune host B cells. Donor T cells that do not bind detectable amounts of host I-A antigens preferentially help nonimmune donor B cells. By contrast, donor T cells that either bind or do not bind host I-A antigens display no H-2-restricted interaction and help both donor and host immune B cells. These data reveal that the Ia antigen-binding specificity of distinct functional subpopulations of alloactivated donor T cells regulates their I-region-restricted (self or allo) helper activity for nonimmune B cells but not immune B cells. Furthermore, they suggest that T cell-macrophage and T cell-B cell collaboration is mediated by a complementary anti-Ia:Ia receptor:ligand type of interaction in which the receptor of a T cell binds to the ligand of an antigen-presenting macrophage and/or B cell.

HLA-A, -B, and -DR specificities on human monocytes

Monocyte-enriched cell suspensions obtained by a plate adherence method from 57 blood donors were typed by microcytotoxicity for HLA-A, -B and -DR determinants. Parallel assays were performed with autologous unfractionated lymphocytes for HLA-A and -B determinants and with autologous B-lymphocytes for HLA-DR determinants. Correlation coefficients (r values) were calculated for nine HLA-A specificities (r greater than 0.79), 16 HLA-B specificities (r greater than 0.56) and seven HLA-DR specificities (r greater than 0.81). For certain HLA-A and -B specificities detection was less readily achieved on monocytes than on autologous lymphocytes. Extra reactions were observed in some instances. With sera defining HLA-DR specificities, monocytes and B-cells showed reactivity of almost identical strength and reliability.

The alloreactivity of human colostral T lymphocytes. II. Specific control of maternal anti-fetal mixed lymphocyte reactivity

Lymphocytes in human colostrum were examined for evidence of alloreactivity specifically directed against the paternal HLA haplotype. Such reactivity was detected using umbilical cord blood leukocytes as stimulator cells in the mixed lymphocyte reaction, but the responses were reduced when compared to those of the same patient's blood lymphocytes. Analysis of this defect determined that only colostral lymphocyte responses to neonatal alloantigens were impaired and that the phenomenon apparently depended on a non-adherent fetal leukocyte for its expression. Attempts to demonstrate directly colostrum or cord blood-derived cell-mediated suppression failed, and the results suggest that a classical T suppressor cell is probably not involved. These findings indicate that human colostrum contains anti-paternal T cell clones but their reactivity is specifically abrogated when cultured with fetal leukocytes.

Evidence for depletion of Ia+ macrophages and associated immunosuppression in African trypanosomiasis

The percentage of Ia antigen-bearing (Ia+) macrophages was significantly lower in mice infected with Trypanosoma rhodesiense than in normal controls. The degree of difference varied with the source of macrophages and time course of infection. The percentage of Ia+ macrophages isolated from spleens 10 days after infection was 71% of that in the controls, and depletion continued until Ia+ macrophages were almost undetectable 30 days after infection. The rate of depletion was slower in the peritoneal cavity. In contrast, Ia+ macrophages were not significantly depleted from the lymph nodes until 30 days after infection. The ability of macrophages from trypanosome-infected mice to present listerial antigen to sensitized T cells was significantly lower than in controls. Immune T cells had significantly less ability (43% of controls) to incorporate thymidine when exposed to splenic macrophages from infected mice during the early stage of disease. This loss of antigen presentation increased during the course of infection. Peritoneal macrophages also exhibited an early loss of ability to present antigen, but no significant decline occurred thereafter. No significant loss of antigen had occurred in the lymph node macrophages 10 days after infection, but during the later stages of the disease a significant loss was detected. Treatment of macrophages from infected and control mice with anti-Iab serum and complement inhibited their ability to present antigen. Our results demonstrate that Ia+ macrophages and their distribution can influence the ability of infected animals to process antigens and may therefore account in part for the immunosuppression observed in trypanosomiasis.

The peritoneal antigen-presenting macrophage: control and immunogenic properties of distinct subpopulations

The control of the immunogenic antigen-presenting capacity of different subpopulations of thioglycollate-induced peritoneal macrophages had been investigated. The experiments revealed the existence of two major subpopulations of macrophages, only one of which was highly efficient in educating antigen-specific T cells. The other subpopulation, while highly phagocytic, was devoid of antigen-presenting capacity. Further analysis, using specific antisera directed at H-2I region gene products, revealed that the immunogenic antigen-presenting population expressed H-2I region-controlled membrane antigens. Searching for cellular elements which control the differentiation of this antigen-presenting macrophage subpopulation, it was found that its function was strictly controlled by T cells. T cell-deficient mice (nu/nu) failed to generate a functional antigen-presenting macrophage subpopulation. Transplantation of mature T lymphocytes to T cell-deprived mice restored the immunogenic function of their antigen-presenting macrophage subpopulation. Transplantation of mature T lymphocytes to T cell-deprived mice restored the immunogenic function of their antigen-presenting macrophages. The results obtained suggest the existence of heterogeneity of functions among macrophage subpopulations and add a new regulatory function for T cells.

A non-T:non-B cell bears I-A, I-E, I-J, and Tla (Qa-1?) determinants

A non-T:non-B accessory cell in peritoneal washout or spleen-cell suspensions facilitates T-cell proliferative responses to the mitogen, concanavalin A. Utilizing monoclonal antibody, we show that this accessory cell bears the same I-A- and I-E-subregion controlled determinants as found on B cells. In addition, the same accessory cell bears a Tla(Qa-1?)-region and an I-J-subregion controlled determinant. This I-J determinant is also present on splenic accessory cells involved in in vitro antibody responses to sheep red blood cells. Data in a companion paper show that not all anti-I-J sera contain antibody reactive with the accessory cell, and suggest that T cells involved in the generation of suppressor activity and accessory cells bear different I-J-subregion controlled determinants.

Langerhans cells as macrophages in skin and lymphoid organs

Properties of epidermal Langerhans cell were compared with those of a number of other dendritic cells in lymphoid organs and of mononuclear phagocytes. Among the dendritic "reticulum" cells included were indeterminate cells from the epidermis, interdigitating "reticulum" cells from T-dependent areas of lymphoid tissue and thymus, follicular dendritic cells of Nossal, and the dendritic cells described by Steinman and Cohn. Interdigitating cells with typical Birbeck granules, in the thymus and in the paracortices of lymph nodes, which are morphologically indistinguishable from Langerhans cells and indeterminate dendritic cells in the epidermis, appear to belong to the same system and possibly represent a subpopulation of "macrophages." On the basis of their similarity to these other dendritic cells, we believe Langerhans cells may function in antigen presentation, lymphokine production, provision of a microenvironment for T lymphocytes, and prostaglandin secretion.