The Human la System

Lymphocyte markers in health and disease

In the 7 years since the last review of lymphocyte markers, written by Tomasi and Stobo, appeared in this journal, there has been a revolution in the diversity and sophistication of immunologic tests directly applicable to investigations of clinical disorders. The promise of such procedures and their allied genetic and monoclonal antibody probes in aiding the classification, early recognition, and therapy of hematologic malignancies, autoimmune disorders, and infectious diseases now is approaching fruition. A synopsis of those assays in vitro and in vivo, together with the primary immune cell subsets they define, is given in Table 12. A grasp of the basic mechanisms underlying them should permit their judicious use, as they are requested either through the clinical laboratory (the initial screen) or as they are complemented by more complex studies obtained through university-affiliated immunology centers (further workup). In this manner, clinically relevant information for the diagnosis and treatment of disorders of immune function will be realized.

Differential effect of monoclonal anti-DR antibody on monocytes in antigen- and mitogen-stimulated responses: mechanism of inhibition and relationship to interleukin 1 secretion

A differential role for DR antigens on monocytes in antigen-stimulated as opposed to mitogen-stimulated human lymphocyte responses has been observed. A monoclonal anti-DR antibody used to treat monocytes caused inhibition of antigen-induced T-cell responses and of T-cell-dependent B-cell responses. However, anti-DR antibody treatment of monocytes did not inhibit mitogen-induced responses. Anti-DR treatment of monocytes did not induce suppression, as antigen-induced responses could be reconstituted with untreated monocytes. Anti-DR treatment of monocytes did not merely block interleukin 1 (IL-1) secretion since addition of IL-1 could not restore antigen-induced responses. Monoclonal anti-DR antibody did not directly inhibit monocyte secretion of IL-1. DR-negative monocytes, selected by antibody and complement, could not present antigen, even though they were capable of secreting IL-1. Thus, this monoclonal anti-DR antibody sterically blocks antigen presentation by monocytes without induction of suppression or inhibition of IL-1 secretion. Monocyte DR antigens appear essential for stimulation of antigen-induced responses, but DR antigens on monocytes may not be essential for mitogen-stimulated responses and do not appear to be related to the ability of monocytes to secrete IL-1.

Expression of major histocompatibility antigens and nature of inflammatory cellular infiltrate in ovarian neoplasms

Expression of histocompatibility antigens and the intensity of inflammatory cellular infiltrate were evaluated in frozen tissue sections from 70 human ovarian tumors and six normal ovaries using monoclonal antibodies and an avidin-biotin immunoperoxidase technique. In the normal human ovary, surface epithelial cells, mature granulosa cells and lutein cells reacted with anti-HLA-A,B,C (HLA) and beta2-microglobulin antibodies but not with anti-Ia (Ia-like, HLA-DR). Stromal cells and granulosa cells of the primordial follicles did not react with any of the antibodies. Among the neoplasms examined, all benign epithelial tumors, 86% of borderline an 81% of malignant epithelial tumors reacted with anti-HLA and/or beta2-microglobulin antibodies. HLA-negative epithelial tumors were of serous or endometrioid types. Although Ia was not found in normal ovarian surface epithelium, the antigen could be detected in 44% of benign, and 43% of borderline and malignant epithelial ovarian tumors. Mononuclear cellular infiltrate was generally scarce in ovarian tumors and consisted mainly of T cells. Malignant epithelial tumors contained significantly more T cells than did benign tumors. More T cells were observed in HLA-positive ovarian tumors than in HLA-negative neoplasms, but the difference did not achieve statistical significance. No correlation could be found between Ia expression and the intensity of T-cell infiltrate. Significantly more T8 and Leu-3a-positive cells were found in the tumor stroma than amongst neoplastic cells. HNK-I-positive natural killer cells, OK-MI-positive macrophages and BI-positive B lymphocytes were rarely encountered either in the tumor stroma or between adjacent tumor cells.

Complement receptor distinguishes between two subsets of large granular lymphocytes with different natural killer activity and cytochemical and ultrastructural features

Human peripheral blood large granular lymphocytes (LGL)--that is, cells with intracytoplasmic azurophilic (electron-dense) granules, with a positivity for the cytochemical localization of certain acid hydrolases, and with avid surface receptors for the Fc portion of IgG--have been purified on Percoll density gradients. Approximately 30% of these cells expressed receptors for the third complement component (C3R). They were separated into C3R-positive and C3R-negative cells. C3R+ cells had a significantly greater natural killer (NK) activity against K562 target cells than C3R+ cells. This difference was unrelated to the presence in the C3R+ cells of a contaminant cell type incapable of NK activity, since cytochemical and ultrastructural analysis revealed that C3R+ and C3R- fractions contained comparable LGL numbers. Agarose cytotoxicity assays at the single-cell level demonstrated that C3R+ LGL contained a large number of cells that bound to but did not lyse the target. The remaining fully cytotoxic C3R+ LGL had, however, the same killing and recycling properties as the cells from the C3R fraction. Electron microscopy and cytochemical studies showed that C3R+ cells had fewer electron-dense granules than C3R cells and stained more faintly for the localization of alpha-naphtyl acetate esterase. In contrast to C3R cells, C3R+ LGL displayed morphological features suggesting that an active process of granule formation was taking place. Taken together, the data indicate that C3R+ cells represent a discrete subset or a maturational stage of LGL.

The reactivity of Reed-Sternberg cells with monoclonal antisera at thin section and ultrastructural levels

In an attempt to improve the morphology of Reed-Sternberg cells after immunochemical procedures, the biotin-avidin technique has been used. Satisfactory morphology was obtained at the level of both light and electron microscopy. Reed-Sternberg cells failed to react with a monoclonal antimonocyte serum but gave positive results with anti-1a and FMC7, a monoclonal anti-B cell serum. Positive results were also obtained with FMC1 and B1 both of which are monoclonal B cell antisera.

HLA-DS molecules and their relation to supertypic specificities

We have analyzed the structures of HLA-DS molecules from DR1, 2, 3, 4, 5, and 7 cell lines by two-dimensional gel electrophoresis and examined the relationship of HLA-DS molecules to those expressing the supertypic specificities MT1, MB3, and MT3. These studies have allowed us to conclude that the HLA-DS locus is as polymorphic as HLA-DR and that the MT1 and MB3 supertypic specificities reside on DS molecules. Furthermore, MT1 molecules from DR1, DR2, and DRw6 cell lines are structurally different as are MB3 molecules from DR4 and DR5 cell lines. In addition, studies using two MT3 specific reagents, a monoclonal antibody, 109d6, and an alloantiserum, Hon, suggest that MT3 is a cross-reactive determinant present on products of two different loci: a DS4 molecule and a DR7-like molecule.

Analysis of T cell subsets in the peripheral blood and synovial fluid of patients with rheumatoid arthritis by means of monoclonal antibodies

In an attempt to define the immunoregulatory mechanisms operating in rheumatoid arthritis we have enumerated T cell subsets in the peripheral blood and synovial fluid of patients with this disease. The peripheral blood analysis revealed an elevation of the ratio of inducer T cells (OKT4 positive) to suppressor/cytotoxic T cells (OKT5 positive) in patients with clinically active rheumatoid arthritis when compared with normal persons. This was due to a reduction in the percentage of suppressor/cytotoxic T lymphocytes in these patients. The synovial fluid in rheumatoid arthritis differed from the peripheral blood in 2 respects. Firstly, synovial fluid was characterised by a lower helper: suppressor ratio due to an increased number of suppressor/cytotoxic cells, and, secondly, it contained an increased number of activated T cells bearing HLA DR antigens. The majority of these activated T cells belonged to the helper/inducer T cell subset.

Genetically regulated human (T,G)-A-L specific helper T cell replacing factors possess HLA-DR and VH determinants

Human (T,G)-A-L specific T cell helper factors secreted by in vitro activated peripheral blood lymphocytes of normal donors were characterized. Factors were passed through columns of Sepharose coupled either to antibodies against human immunoglobulin or antibodies against the variable region of the heavy (VH) and light (VL) chains of human immunoglobulin. In addition, the same factors were applied to columns of Sepharose coupled to anti-HLA-DR antibodies or to monoclonal antibodies against human Ia or beta 2-microglobulin. The activity of the antigen specific factors was removed by the anti-VH antibodies and not by anti-VL or anti-human immunoglobulin antibodies. The factors passed through Sepharose coupled to anti-DR antibodies could be removed and eluted from columns of anti-DR antibodies relevant to the donors' DR antigens. The same factors were also removed by a monoclonal antibody (anti-Ia) which recognizes a monomorphic determinant on HLA-DR, but not by monoclonal anti-beta 2-microglobulin. The results suggest that the genetically regulated (T,G)-A-L specific helper factors possess HLA-DR as well as VH determinants in their active moiety.

Expression of HLA-DR antigens at the surface of mouse L cells co-transfected with cloned human genes

The H-2 I region in the mouse and the HLA-D region in humans contain a set of polymorphic genes which encode Ia antigens and control the immune response. Cloned genes for the different polypeptide chains of one of the human Ia antigens, HLA-DR, have been used for the co-transformation of mouse L cells. Expression of HLA-DR antigens at the surface of transfected mouse cells has been documented with monoclonal antibodies.

Cell lineage in lymphoproliferative disease

Surface marker techniques have made a major contribution to the understanding and classification of lymphoproliferative disorders by permitting the determination of B- and T-cell lineage. The frequent malignant proliferations of B lymphocytes are identified by the presence of surface immunoglobulin of a single light-chain type; Ia-like (HLA-DR) antigen is present as well. While most T-cell proliferations exhibit the classic receptor for sheep erythrocytes, commercially available monoclonal antisera permit the secure identification of T cells and their subclassification into inducer-helper and cytotoxic-suppressor subsets. Surface markers have also allowed the separation of a fraction of patients with acute lymphocytic leukemia whose cells have T-lymphocyte markers from the majority whose cells show subtle evidence of early B-cell differentiation.

Enhanced expression of human Ia antigens by chronic lymphocytic leukemia cells following treatment with 12-O-tetradecanoylphorbol-13-acetate

Using a panel of monoclonal antibodies which detect framework determinants of human-Ia alpha and beta polypeptides and the DC-specific monoclonal antibody Genox 353, the in vitro effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the expression of Ia antigens by cells from chronic lymphocytic leukemia (CLL) patients have been studied. In all subjects studied a great increase in expression of framework Ia determinants was found following culture of CLL cells for 90 h with TPA at 10(-7) g/ml. TPA treatment of CLL cells also induced increased expression of Genox 353+ antigens, in some cases where Genox 353 binding was either negligible or not detectable in cells cultured in the absence of TPA.

In vitro analysis of lymphocytes: markers and functions

Current dermatologic literature is becoming replete with articles elucidating current concepts in the pathophysiology of lymphocytic diseases. Much of this knowledge emanates from the increasingly sophisticated and complex methods of identifying lymphocytes. No longer does it suffice to know that B lymphocytes or T lymphocytes are present, but rather the key information involves knowing what subsets of these cells are present and/or their functional status. The reader attempting to assimilate all this information is thus confronted with an overwhelming, as well as frequently changing, array of analytic methods. This paper is presented as a review of thinking, principles, and methods employed in research on lymphocytic disease.

Differential expression of HLA-DR and DR-linked determinants on human leukemias and lymphoid cells

Leukemic and normal hemopoietic cells were examined with the monoclonal anti-bodies DA2 and Genox 353 for the presence of HLA-DR and DR-linked (DC/MB) determinants, respectively. Although most non-T acute leukemias and leukemic cell lines expressed the monomorphic DR determinant detected by DA2, fewer than expected expressed the DR-linked polymorphic specificity detected by Genox 353. TdT+ lymphoid precursors from normal bone marrow were also DA2+ but Genox 353-. T cells and thymocytes which were DA2-, Genox 353- became DA2+, Genox 353+ after activation in vitro. Immunoprecipitation using DA2 and Genox 353 gave bands on polyacrylamide gel-electrophoresis which were of different molecular weights. In addition, DA2 could absorb out Genox 353 determinants from a cell lysate whereas Genox 353 could not absorb out DA2 determinants. It is concluded that DA2 and Genox 353 detect HLA-DR and DR-linked (DC1/MB1) determinants, respectively, and that these are differentially expressed on hemopoietic cells during differentiation.

Human sympathetic ophthalmia. An analysis of the inflammatory infiltrate by hybridoma-monoclonal antibodies, immunochemistry, and correlative electron microscopy

A case of human sympathetic ophthalmia, enucleated after surgical trauma, was studied by means of hybridoma-derived monoclonal antibodies, histochemistry, and transmission electron microscopy. The choroidal infiltrate was composed predominantly of T-lymphocytes of the suppressor/cytotoxic subset (OKT8+); only 5% of the cells were immunoglobulin-producing B-lymphocytes (kappa or lambda light chain positive), thereby explaining the well-known paucity of plasma cells in the infiltrate. The epithelioid cells and phagocytic histiocytes in the choroid were la+ and OKM1+, antigenic determinants specific for bone marrow-derived monocytes, and their cytoplasms exhibited histochemical reactivity for alpha-1-antichymotrypsin and lysozyme. Ultrastructurally, the choroidal epithelioid cells contained single melanin granules in the cytoplasm, but these were membrane-bound and frequently associated with lysosomal material, features militating against these cells being transformed choroidal melanocytes. By means of immunologic and ultrastructural analysis, the Dalen-Fuchs nodules were found to be composed of a mixture of histiocytes (la+ and OKM1+) and depigmented retinal pigment epithelial cells (la- and OKM1-); the latter cells focally formed desmosomes and displayed inclusions of lipofuscin. Scattered within the Dalen-Fuchs nodules were small numbers of T-lymphocytes of the suppressor/cytotoxic subset. We have concluded that the uveitis and retinal pigment epithelial changes are mediated by a T-cell, delayed hypersensitivity pathogenetic mechanism (cell-mediated immunity), possibly directed at surface membrane antigens that may be shared by photoreceptors, retinal pigment epithelial cells, and choroidal melanocytes.

Blood and lymph node T-lymphocyte subsets in non-Hodgkin lymphomas

Blood and lymph node T-lymphocyte subpopulations have been studied in untreated non-Hodgkin lymphoma (NHL) patients and healthy controls. T-lymphocytes were determined by the E-rosette technique and by OKT3/LEU4 monoclonal antibodies; OKT4/LEU3 and OKT8/LEU2 monoclonal antibodies were used to identify T-cell subsets with helper/inducer and suppressor/cytotoxic activity, respectively. OKT4+ T-cells were low in patients, while OKT8+ T-cell numbers were normal. The OKT4+/OKT8+ blood lymphocyte ratio was below the normal range in about 50% of the patients. The ratio was higher in lymph nodes than in blood of patients and controls. The results may suggest that untreated NHL patients have a reduced pool of T-cells with phenotypic markers of OKT4/LEU3. Monoclonal blood B-lymphocytes were found in 45% of the cases. The presence of such cells in blood was frequently associated with a low OKT4+/OKT8+ ratio.

Endocytosis of class II histocompatibility antigens and formation of intracytoplasmic granules at the final differentiation stage of human B lymphocytes

The expression of histocompatibility antigens was investigated using several human lymphoid cell lines representative of different maturation stages of the B-cell lineage. Class II HLA antigens were found at the surface of all cell lines. However, in the myeloma cell line U266, an intracellular macrovesicular pool of these antigens was found in some cells. It originated from microvesicular endocytosis of the surface antigen, subsequently leading to cells bearing HLA class I but not class II antigens. Since the latter play a major role in cellular interactions regulating B-cell differentiation, this phenomenon may be linked to the final stage of maturation of B lymphocytes into plasma cells.

Ia antigens on non-lymphoid tissues their origins and functions

Ia molecules are encoded in the 1 region of the mouse major histocompatibility complex (MIX) and expressed as surface antigens on certain immunologically active cells (reviewed in Ref. 1). B cells, subsets of T helper and T suppressor cells and accessory, antigen-presenting cells are Ia-positive (Ia+) while T killer cells and natural killer cells are not. This article discusses the nature and function of Ia+ cells found in non-lymphoid tissues, some of which are immunologically involved while others are not obviously so.

Human MHC class II molecules as differentiation markers

DA6.231 and DA6.164 are mouse monoclonal antibodies that immunoprecipitate HLA-DR-like p34,29 glycoprotein dimers from surface- and metabolically-labeled cells. On lymphoblastoid cell lines the distribution of the 231 epitope is completely nonpolymorphic, while the 164 epitope is present on all cells except on those that are DR7 homozygous. Binding-inhibition studies show that the 231 and 164 epitopes are spatially close to each other when present on the same molecule. The mutual inhibition pattern and the absence of the 164 epitope from the 231+ cells of a few leukemia patients suggest, however, that 231 and 164 epitopes are not invariably present together. Most DR-positive cells possess 231+ and 164+ and 231+ 164- class II molecules in approximately a 2:1 ratio. This has been confirmed by immune depletion studies. Thus DA6.231 appears to define a supralocus epitope. The 164 epitope may be a marker for a subset of class II molecules exhibiting differential expression on various cell types immortalized by malignant transformation.

Neutrophil granulocytic cell antigen defined by a monoclonal antibody--its distribution within normal haemic and non-haemic tissue

Monoclonal antibodies were raised against normal human bone marrow cells. One of the antibodies obtained, monoclonal antibody 3C4 (MA 3C4), the subject of this paper, was characterised by immunofluorescence studies with viable normal peripheral blood and bone marrow cells and by immunoperoxidase studies using paraffin sections. In bone marrow and peripheral blood MA 3C4 reacts selectively with cells of late neutrophilic granulopoiesis (myelocytes, metamyelocytes, and neutrophilic granulocytes). Cells of erythropoiesis, thrombopoiesis and lymphopoiesis are negative. In lymph node and spleen only neutrophils react with MA 3C4. In non-haemic tissue reactivity was seen with epithelial cells of a variety of different gland ducts. Thus the antigen detected by MA 3C4 can serve as a marker for neutrophil differentiation in normal haemopoiesis and as a marker for ductal epithelial cells of a variety of organs within non-haemic tissue. The antigen is formalin-resistant and can be detected in paraffin sections. The antibody thus appears to be a valuable reagent for both haematological research and for routine pathology.

Modulation of in vitro BFU-E growth by normal Ia-positive T cells is restricted by HLA-DR

The in vitro growth of immature erythroid precursors, assayed as burst forming units (BFU-E), can be enhanced by co-culturing with normal T cells. The growth enhancing effect of normal T cells, however, was shown to be the outcome of at least two functionally distinct subpopulations, one that enhances burst formation and one that limits it. It appears that the T cell population limiting growth enhancement of the erythroid precursors expresses 'Ia-like' antigen (Ia+) because treatment of T cells with anti-Ia antibody and complement significantly increased the ability of the remaining T cells to stimulate antologous BFU-E growth. As BFU-E also seem to express Ia, the inhibiting effect of certain T cells on BFU-E growth may involve the Ia molecule. We show here that the inhibitory effect of Ia+ T cells on BFU-E growth is genetically restricted to cell combinations which are phenotypically identical for at least one HLA-DR (Ia-like) antigen.

DR antigen positive monocyte-macrophages control granulocyte-macrophage colony-stimulating activity and burst promoting activity elaboration in man

To investigate the mechanisms that modulate granulocyte-macrophage colony-stimulating activity (GM-CSA) and burst promoting activity (BPA) elaboration, we studied human peripheral blood-derived monocyte-macrophage (M0) and T-lymphocyte (TL) interaction. Coincubation of live M0 with autologous TL at a 1:3 ratio in the presence of 1% phytohemagglutinin synergistically increased GM-CSA (6 of 6 experiments) and BPA (4 of 6 experiments) (P less than 0.002). Prior treatment of M0 with cycloheximide or actinomycin D significantly (P less than 0.002) diminished this M0's capacity to collaborate with TL. Mitomycin C treatment did not. Live M0 also enhanced TL-derived GM-CSA (P less than 0.002) and BPA (P less than 0.001). This enhancement was again compromised by prior cycloheximide or actinomycin D treatment, but not by mitomycin C treatment. Further experiments in which we blocked DR antigen on M0 membrane with monoclonal anti-DR antibodies suggested that M0 required their membrane DR antigen to collaborate with TL in elaborating GM-CSA and BPA.

Analysis of DR-like molecules on a marmoset Epstein-Barr virus-induced cell line using a monomorphic anti-human HLA-DR monoclonal antibody

Mouse anti-HLA D region-related (DR) monoclonal antibodies have been found to cross-react with peripheral blood leukocytes from one primate species, the common marmoset (Callithrix jacchus). Immunoprecipitates of radioactively labeled cells extracted from a marmoset Epstein-Barr virus-induced cell line were analyzed by one- and two-dimensional gel electrophoresis and compared with the DR antigens of a human lymphoblastoid B cell line. Two chains of estimated molecular weights of 34 000 (alpha) and 28 000 (beta), similar to the human alpha and beta chains, have been observed in marmoset immunoprecipitates. Additionally, a set of spots located in the same area as the set of invariant spots found in human HLA-DR antigens is shown by two-dimensional gel electrophoresis. Thus, cross-reacting anti-human HLA-DR monoclonal antibodies could be used to analyze the expression and the structure of marmoset DR-like antigens.

Immune functions of human synovial cells. Phenotypic and T cell regulatory properties of macrophage-like cells that express HLA-DR

Normal and rheumatoid synovial cells have been analyzed in frozen sections and in suspension. HLA-DR-expressing, macrophage-like cells are demonstrated in normal synovial intima and in rheumatoid tissue. Suspended normal synoviocytes equaled peripheral blood non-T lymphocytes as stimulators of mixed lymphocyte reactions, whereas adherent rheumatoid synovial cells were extremely efficient as such stimulators and in presenting soluble antigens to autologous T lymphocytes. This HLA-DR-dependent T lymphocyte regulation might provide a cellular basis for the HLA-D haplotype-arthritis associations.

T-cell chronic lymphocytic leukemia. Report of a case studied with monoclonal antibody

A previously healthy 74 year old woman presented with T-cell chronic lymphocytic leukemia, lymphadenopathy, hepatosplenomegaly and a mediastinal mass. The circulating lymphocytes were small to medium in size (some with convoluted nuclei) and W rosette-positive; they could be assigned to the inducer-helper subset of T cells with the acid of monoclonal antisera. These cells reacted with OKT3, which detects peripheral T cells; OKT4, which detects the inducer-helper subset of T cells; and OKT11, which detects the sheep cell receptor. It is noteworthy that they were also positive for the la-like antigen found on T cells only after activation. Microscopic examination of a lymph node biopsy specimen revealed a diffuse pattern of pleomorphic large cells characteristic of the T-cell lymphomas and lymphocytic leukemias reported from Japan. However, the lymph node cells lacked the T-cell differentiation antigens present on the circulating lymphocytes. The findings in this case provide insight into the pathogenesis of this unusual disorder and are relevant to our understanding of the spectrum of surface antigens in the more common malignant lymphomas.

Human skin cells synthesize HLA-DR molecules of the same charge and molecular weight as those synthesized by autologous lymphocytes

Between 5 and 14% of human skin cells, separated by trypsinization, express HLA-DR antigen as detected by indirect immunofluorescence with monoclonal anti-DR antibody. To determine the source and structure of these DR molecules, skin cell suspensions were biosynthetically labeled with 35S-methionine and the radiolabeled DR molecules were analyzed by the method of two-dimensional polyacrylamide gel electrophoresis. The results indicated the presence of heavy, intermediate, and light chains indistinguishable from those of B lymphocyte DR. Gels in which DR immunoprecipitates from skin cells and autologous lymphocytes were run simultaneously confirmed this finding. Thus, skin cells and lymphocytes synthesize HLA-DR antigen of identical charge and molecular weight.

Unusual distribution of Ia-like antigens on canine lymphocytes

The murine monoclonal antibody 7.2, specific for a framework determinant of human Ia antigens, cross-reacts with canine cell membranes recognizing a bimolecular complex (29,000 and 34,000 daltons) similar to that described in man. We investigated the distribution of these Ia-like antigens on mononuclear cells in peripheral blood, thoracic-duct lymph, marrow, alveolar lavage fluids, lymph nodes, and thymuses from normal dogs. By complement-mediated cytotoxicity and indirect immunofluorescence, virtually all lymphocytes expressing surface immunoglobulin (B lymphocytes), monocytes/macrophages, dendritic cells, and many thymus-epithelial cells were Ia-positive. Furthermore, most non-B-lymphocytes in peripheral blood, thoracic-duct lymph, and lymph nodes expressed Ia antigens. Alveolar (T) lymphocytes and most thymocytes were Ia-negative. Generally, fluorescence intensity was higher on monocytes/macrophages and B lymphocytes than on non-B-lymphocytes. In mixed leukocyte cultures and concanavalin A-induced blastogenesis assays, treatment of responder cells with antibody 7.2 and complement abolished proliferation. Proliferative responses could not be restored by adding untreated accessory cells, indicating that cytolytic treatment had eliminated responder T-lymphocytes. However, addition of antibody alone to cultures had no significant effect. These studies indicate that most mature canine T-lymphocytes express Ia-like antigens. Whether this is an intrinsic property of canine cells or possibly related to continuous in vivo stimulation remains to be determined.

Expression of DR antigens in freshly frozen human tumors

DR antigens are thought to function as differentiation antigens and to restrict immune recognition between T cells and B cells, monocyte/macrophages, Langerhan's cells, and endothelial cells. These antigens are commonly found on tissue culture lines from metastatic melanomas and tumors of lymphocyte derivation but are notably uncommon on cell lines from other malignancies. Using frozen tissue sections, a monoclonal antibody (WI 691-13-17) known to detect an epitope common to all DR alloantigens on the beta (light) chain of DR antigens, and a two-step indirect immunoperoxidase technique, DR antigens were found on all metastatic lesions tested and on many primary tumors and their histogenetic precursors. The technique of using monoclonal antibodies in indirect immunoperoxidase staining of freshly frozen tissue allows individual cells to be assessed for antigen expression and presumably more accurately reflects in vivo antigen expression than results obtained from cells selected by tissue culture methods.

Demonstration of Ia antigens on certain dendritic cells and on a novel elongate cell found in human synovial tissue

Adherent cells from dissociated human synovial tissue obtained at surgery contain two types of distinctive cells with one or more elongated branching processes that strongly express Ia antigens. One type of cell with Ia antigens is non-phagocytic and resembles the murine dendritic cell. It is primarily found in patients with rheumatoid arthritis and accounts for a considerable proportion of the identifiable cells with a stellate or dendritic morphology. The expression of Ia antigens progressively diminished in culture. The second type of novel cell with Ia antigens was highly elongate and fibroblastoid. It was readily obtained from patients with osteoarthritis. The cell was frequently characterized by a blunt-ended filopodium-like process at one pole of the cell, one or two tapering processes, and zones of microvilli. Evidence was obtained suggesting that this cell, which might otherwise be considered fibroblast-like, is in the mononuclear phagocyte lineage.

Genetic aspects of rheumatoid arthritis

Studies on the population of patients with rheumatoid arthritis and families with multiple cases of rheumatoid arthritis have provided definite evidence that susceptibility to the disease is determined both by genetic factors associated with alleles of the major histocompatibility complex as well as environmental factors. The development of seropositive, but not seronegative rheumatoid arthritis is associated with the presence in an individual of the Ia alloantigen HLA-DR4. This association is common to all major ethnic groups. Some evidence exists that this association is stronger in patients that have more severe disease but this fact requires further study. The fraction of the seropositive patients with rheumatoid arthritis that lack HLA-DR4 has not been well characterized. The occurrence of certain untoward side effects of therapy is influenced by the presence of HLA-DR2 or HLA-DR3. Family studies emphasize the association with HLA-DR4, and indicate that the disease has a dominant mode of inheritance with partial penetrance. The inheritance of susceptibility appeared, at least in some families, to be primarily associated with the inheritance of HLA-DR4 itself and not well explained by a hypothetical disease susceptibility gene present at low frequency and associated in linkage disequilibrium with a HLA-DR4 marker. However, in others different mechanisms appeared more likely. A model of two MHC genes involved in influencing disease susceptibility is postulated. Speculations concerning the primary disease mechanism are presented involving abnormalities of IR genes, general immune regulation, and factors outside of the immune system.

Immunoregulation

The immune system of higher vertebrates is a complex network of separate, interacting cell populations, each ontogenetically endowed with specific regulatory (inductive or suppressive) or effector functions. The products of at least two major gene clusters-the immunoglobulin structural genes and the genes of the major histocompatibility complex-are expressed as active and passive recognition structures on cells of the immune system and at least some of their secreted products. Macrophages play a critical role in the initiation of immune responses. Regulatory subsets of thymus-derived lymphocytes interact with macrophages and with each other in the control of immune effector cells. At every level of the immune response, cell interactions require that these regulatory cells recognize gene products of the major histocompatibility complex. Due to recent technical advances, rapid progress is being made in identifying subsets of human immunoregulatory cells; those identified to date show strong functional homology to previously well characterized murine cell subsets.