HLA-D/DR restriction of macrophage-dependent antigen activation of immune T lymphocytes: cross-reacting allogeneic HLA-D/DR may partly substitute for self HLA-D/DR

Bone Marrow Mesenchymal Stem Cell-Derived Exosomal MicroRNA-126-3p Inhibits Pancreatic Cancer Development by Targeting ADAM9

Pancreatic cancer is a lethal malignancy with relatively few effective therapies. Recent investigations have highlighted the role of microRNAs (miRNAs) as crucial regulators in various tumor processes including tumor progression. Hence the current study aimed to investigate the role of bone marrow mesenchymal stem cell (BMSC)-derived exosomal microRNA-126-3p (miR-126-3p) in pancreatic cancer. Initially, miRNA candidates and related genes associated with pancreatic cancer were screened. PANC-1 cells were transfected with miR-126-3p or silenced a disintegrin and a metalloproteinase-9 (ADAM9) to examine their regulatory roles in pancreatic cancer cells. Additionally, exosomes derived from BMSCs were isolated and co-cultured with pancreatic cancer cells to elucidate the effects of exosomes in pancreatic cancer. Furthermore, the effects of overexpressed miR-126-3p derived from BMSCs exosomes on proliferation, migration, invasion, apoptosis, tumor growth, and metastasis of pancreatic cancer cells were analyzed in connection with lentiviral packaged miR-126-3p in vivo. Restored miR-126-3p was observed to suppress pancreatic cancer through downregulating ADAM9. Notably, overexpressed miR-126-3p derived from BMSCs exosomes inhibited the proliferation, invasion, and metastasis of pancreatic cancer cells, and promoted their apoptosis both in vitro and in vivo. Taken together, the key findings of the study indicated that overexpressed miR-126-3p derived from BMSCs exosomes inhibited the development of pancreatic cancer through the downregulation of ADAM9, highlighting the potential of miR-126-3p as a novel biomarker for pancreatic cancer treatment.

Class II major histocompatibility complex restriction of human T cell responses to short ragweed allergen, Amb a V

Although T cells are known to play a crucial role in the induction of IgE synthesis, the class II major histocompatibility complex (MHC) restriction of aeroallergen-induced T cell responses in humans is incompletely defined. We have previously shown that, in allergic Caucasoid individuals, HLA-DR2 and Dw2 (DR2.2) is strongly associated with specific IgE and IgG antibody responses to highly purified Ambrosia (ragweed) allergen, Amb a V, from the artemisiifolia (short) species. For example, 95% of IgE antibody responders to Amb a V were typed as DR2.2. In a novel study of the genetic control of T cell responses to the Amb a V allergen, we have investigated the MHC class II restriction specificity of three CD4, Amb a V-specific T cell clones derived from a DR2.2+ atopic patient, and a polyclonal Amb a V-reactive T cell line from another DR2.2+ patient. We observed proliferative responses of all three clones to Amb a V only when either HLA-DR2.2 or DR2, Dw12 (DR2.12; found on Mongoloid populations) was present on the antigen-presenting cells, regardless of the HLA-DQ phenotype of the cells. Moreover, the responses of T cell line and clones were abolished by anti-DR but not by anti-DQ nor by anti-DP monoclonal antibodies, and, significantly, anti-DR alpha/beta I2 (anti-DR alpha /beta Iw15/w16; anti-"DR2b") monoclonal antibody blocked, in a dose-dependent manner, the cloned T cell responses to Amb a V. These findings demonstrate that DR alpha/beta I2.2 (DR alpha/beta I1501) and DR alpha/beta I2.12 (DR alpha/beta I1502) are functional in the restriction of the T cell recognition of Amb a V. These findings also illustrate the power of the allergy model for definitive investigation of the molecular basis of the human immune response.

HLA class II restriction specificity of Dermatophagoides spp. reactive T lymphocyte clones that support IgE synthesis

The results of recent experiments investigating the restriction specificity of cross-reactive, or Dermatophagoides farinae-specific, T cell clones isolated from an atopic individual with perennial rhinitis are reviewed. The restriction specificity was examined using serological inhibition, allogeneic presenting cells and murine fibroblasts expressing HLA-D region products. Although serological inhibition studies suggested that DR class II proteins were the major restriction elements used, the patterns of recognition observed with the allogeneic cell panel were complex, generally failing to correlate with the serologically defined MHC class II specificities. Analysis of the restriction patterns indicated that the majority of the T cell clones were restricted by DR beta III gene products and this was confirmed using murine fibroblasts expressing DRw52. DR beta I gene products functioned as restriction elements in the recognition of house dust mite allergen by the other clones. In an in-vitro model of allergen-dependent IgE synthesis, both DR beta I and DR beta III class II restricted T cells could be shown to provide functional help for IgE synthesized by autologous B cell-enriched populations.

Antigen presentation by human antigen-presenting cells to antigen-specific xenogeneic murine T cells

Successful antigen presentation by xenogeneic human antigen-presenting cells (APC) to stimulate the proliferation of antigen-specific, keyhole limpet hemocyanin (KLH)-specific, ovalbumin (OVA)-specific, and purified protein derivative of Mycobacterium tuberculosis (PPD)-specific murine T cells was observed. Evidence indicating a direct cell interaction between antigen-specific murine T cells and xenogeneic human APC was given by experiments using antigen-specific murine T cell clones. The OVA-specific B10.S(9R) T cell line (9-0-A1) and PPD-specific B10.A(4R) T cell line (4-P-1) were stimulated by both xenogeneic human APC and murine APC from syngeneic or I-A compatible strains, while the PPD-specific human T cell line (Y-P-5) was stimulated by autologous human APC but not by murine APC. Anti-HLA-DR monoclonal antibodies (MoAb) blocked the xenogeneic human APC-antigen-specific murine T cell clone interaction. Thus, human xenogeneic APC can stimulate antigen-specific murine T cells through HLA-DR molecules in the same manner as syngeneic murine APC do through Ia molecules coded for by the I region of the H-2 complex, while murine APC failed to present antigen to stimulate human antigen-specific T cells.

Dendritic cells from human rheumatoid synovial inflammatory tissue and peripheral blood as accessory cells in mitogen stimulation of T lymphocytes

Dendritic cells (DC) were purified from the peripheral blood (PB) of normal individuals and from the synovial fluid (SF) and synovial tissue (ST) of patients with rheumatoid arthritis. These cells are strongly HLA-DR positive and lack B-cell, T-cell, and monocyte markers as well as Birbeck granules. The DC were compared with monocytes and non-T cells from PB for their ability to act as accessory cells for T-cell responses to concanavalin A (Con A) and phytohaemagglutinin (PHA). DC from PB, SF and ST were much more efficient accessory cells for the mitogenic responses than autologous monocytes from PB. The mean PHA responses in cpm obtained with DC from the various compartments were 4-20 times greater than the responses obtained with monocytes from PB. The Con A responses obtained when the various DC populations were used as accessory cells were 3-13 times greater than those obtained with monocytes from PB. The mitogenic responses seen with monocytes were very low. The non-T cells, which comprise a mixture of cells obtained after removal of T cells, also gave low T-cell responses to PHA and Con A compared with DC as accessory cells.

Rheumatoid synovial dendritic cells as stimulators in allogeneic and autologous mixed leukocyte reactions--comparison with autologous monocytes as stimulator cells

Dendritic cells were isolated from peripheral blood, synovial fluid, and synovial tissue of patients with rheumatoid arthritis and from peripheral blood of healthy blood donors on the basis of semiadherence to plastic surfaces. The cells were compared with autologous peripheral blood monocytes with respect to their stimulating capacities in allogeneic and autologous mixed leukocyte reactions (MLR). Dendritic cells from the various compartments stimulated allogeneic T cells 6-14 times more than monocytes did. Dendritic cells also stimulated autologous T cells 10-24 times more than monocytes did. Evidence in favour of the dendritic cell as the major stimulating cell type in MLR was also found in mixed experiments in which various ratios of dendritic cells and monocytes were used as stimulator cells. Furthermore, the activating structures on the dendritic cells seem to be major histocompatibility complex class II antigens, since anti-HLA-DR antibodies inhibited the responses. The results, especially from the autologous MLR, indicate that dendritic cells are important accessory cells for the various immune responses in rheumatoid inflammation.

Detection of HLA restricted anti-minor histocompatibility antigen(s) reactive cells from skin GVHD lesions

Recipients of marrow grafts from HLA-identical, (including MLC non-reactive) sibling donors have a 40-50% incidence of acute graft vs. host disease (GVHD); the involvement of non-HLA linked, minor histocompatibility antigens (miHA) has been implicated. One of the target tissues of GVHD is the skin where morphological analysis of biopsy specimens is often used to support this diagnosis. We have obtained skin biopsy specimens from the site of GVHD lesions, grown the cells in the presence of T cell growth factor (TCGF) and feeder cells, and tested these cultured cells in the primed lymphocyte test (PLT) and cell mediated lympholysis (CML) assay. Five of six cell cultures tested demonstrated secondary proliferative but not cytolytic reactivity; cells from one culture demonstrated both reactivities. The cell culture populations generated are presumably directed against non-HLA antigens, i.e., miHA whose expression is restricted by an HLA antigen of the recipient. The data are consistent with the suggestion that in the majority of these cultures, the restriction element may be a determinant encoded within the HLA-D region: DQ, DR, and possibly DP based on panel testing. Although the number of cases is small, these preliminary data demonstrate the feasibility of this type of culturing system and also suggest that the cellular immunological events leading to the manifestation of skin GVHD lesions may be predominantly a delayed type hypersensitivity reaction.

Development and characterization of interleukin-2-independent antigen-specific human T cell clones that produce multiple lymphokines

The development of antigen-specific T lymphocyte lines and clones has greatly facilitated the investigation of T-cell recognition of and response to foreign antigens. In the present study, human antigen-specific helper T cell lines and clones which are completely independent of exogenous interleukin-2 (IL-2) have been developed by cyclic restimulation with the soluble antigen keyhole limpet hemocyanin (KLH) to which the T cell donor had previously been immunized. These T cells uniformly bear the OKT4 phenotype and were shown to require both histocompatible antigen-presenting cells (APC) and antigen for optimal proliferation. The T cell line was composed of a highly antigen-specific and clonable T cell population. Following four cycles of antigen stimulation, limiting dilution cloning analysis showed a Poisson distribution of clonable T cells with a precursor frequency of 0.62, and from 88 to 92% of viable clones were specific for the stimulating antigen. Individual clones were obtained which recognized KLH with either DR 1 (one parental Ia haplotype of the donor) or DR 2 (the other parental Ia haplotype) allogeneic APC, but not both. Following stimulation with KLH, the T cell clones produced IL-2. Peak amounts of IL-2 were assayable in the first 6 to 24 hr after stimulation. In contrast, virtually no IL-2 was detectable in supernatants at 72 to 96 hr, suggesting autoutilization by the proliferating T cells. In addition, some clones were also capable of producing both B cell growth factor and IL-2 following KLH stimulation. These IL-2-independent T cells appeared to be derived from a discrete Leu 8-negative subclass of T4+ cells and expressed the full complement of Ia antigen of the donor. Thus, soluble antigen-specific human helper T cell clones have been produced which can be maintained in the absence of exogenous IL-2, elaborate their own growth factors and other immunoregulatory lymphokines, and show fine DR-related restriction to either one or the other parental DR haplotypes in antigen-stimulated proliferative responses.

Parasite antigen-specific human T cell lines and clones. Major histocompatibility complex restriction and B cell helper function

The development of T lymphocyte lines and clones of defined specificity has become an important method for investigating both T cell recognition of foreign antigens as well as T cell influence on B cells. In the present study, human antigen-specific T cell lines and clones have been derived from a patient with a naturally acquired filarial infection. These T cells are of the helper phenotype (Leu 1+, Leu 2-, Leu 3+) and are independent of exogenous interleukin-2. Furthermore, these T cells have been shown to require both antigen-presenting cells and antigen for optimal proliferation. Helper function mediated by these T cells as manifested by the in vitro induction of parasite-specific antibody was antigen-dose dependent, requiring much lower antigen concentrations than those necessary to induce blastogenesis. More importantly, there is an absolute requirement of the T cell line for HLA-DR histocompatible antigen-presenting cells; clones derived from this T cell line show a more specific DR-related restriction--to only one of the two parental DR haplotypes in antigen stimulated proliferative responses. Such parasite antigen specific human helper T cell lines and clones should prove useful in exploring the fine control of the host response to naturally acquired helminth infections. In addition, these long-term T cell lines and clones can provide a potent tool for examining not only the events involved in human T cell responses to parasite antigens, but also into the associated cellular and humoral factors necessary for the B cell responses which follow.

Influenza A hemagglutinin-specific T cell clones strictly restricted by HLA-DR1 or HLA-DR7 molecules

The antigenic specificities, major histocompatibility complex restrictions and functional properties of influenza virus-specific proliferative cloned cell lines have been studied. These lines were specific for the H3 hemagglutinin subtype of influenza A viruses. By using a large panel of HLA-phenotyped antigen-presenting cells, it was found that the polymorphic structures, defined as DR1 and DR7 molecules, or closely associated structures, function as the restricting elements. We excluded for these lines a possible restricting role of supertypic specificities, known cross-reacting elements on DR molecules, or products of other loci in known linkage disequilibrium with the HLA-DR molecules. Such exquisitely restricted clones might be of great help in the class II typing of antigen-presenting cells. Their specific activity was stable for several months. This has allowed the study of some functional properties of these long-term-cultured cloned cell lines: interleukin 2 sensitivity and production, helper function in specific antibody synthesis and ability to stimulate in mixed leukocyte reactions.

Antigen-specific HLA-restricted human T-cell lines. I. An MT3-like restriction determinant distinct from HLA-DR

The results presented provide evidence that the HLA specificity known as MT3, BR4, or Hon7 can serve as a restriction epitope for the proliferation of certain T cells responding to mumps viral antigen. This restriction determinant was found to be HLA-linked in family studies, and to segregate centromeric to a crossover between HLA-B and DR in one family. In the population studied, the specificity was found to be associated with the DR antigens DR4, DR7, and DRw9, which are known to be associated with MT3. The ability of accessory cells to present mumps antigen in the context of this supertypic restriction determinant was blocked by a monoclonal antibody specific for MT3. Since MT3 (BR4, Hon7) has been shown to be expressed on molecules distinct from DR, our experiments suggest that such molecules are functionally important in antigen presentation to T cells.

Human helper T-cell clones that recognize different influenza hemagglutinin determinants are restricted by different HLA-D region epitopes

Human T-lymphocyte clones ( TLCs ) were generated against the hemagglutinin (HA) of A/Texas/1/77 influenza virus by limiting dilution. TLCs were then screened for antigen specificity on chemically synthesized peptides representing the HA1 molecule. It has been hypothesized that different T cells that recognize the identical antigenic determinant are controlled by (restricted by) the same class II epitope. Two TLCs , HA1.4 and HA1.7, both recognized the same HA peptide and in proliferation studies exhibited identical restriction patterns. Two other clones, HA 1.9 and HA 2.43, recognized different HA determinants and also had distinct restriction patterns. Proliferation inhibition studies with monoclonal antibodies against human class II molecules demonstrated three unique patterns of blocking with the clones, suggesting that clones may be restricted to a unique class II epitope depending on the HA determinant recognized. These data can be interpreted as supporting the argument that human immune responses to influenza hemagglutinin are under Ir gene control exerted at the level of the viral antigenic determinant recognized in association with particular D-region restricting elements. The determinant selection and clonal deletion theories are compared for their capacity to best explain these findings.

Class-II HLA restriction of antigen-specific human T-lymphocyte clones. Evidence of restriction elements on both DR and MT molecules

Blast-enriched suspensions of T cells primed for Chlamydia trachomatis antigen were cloned by a limiting dilution technique. The class-II HLA restriction of T-lymphocyte clones (TLC) was studied by using allogeneic antigen-presenting cells (APC) carrying foreign class-II HLA antigens. Most of the TLC were restricted by one or the other of the D/DR determinants of the T-cell donor; that is, they did not respond when antigen was presented by APC expressing foreign D/DR determinants. Furthermore, heterogeneity of the DR4-expressing molecule could be demonstrated by T-cell clones from one person; APC from family members expressing DR4 gave high proliferative responses, whereas no proliferation was observed with most APC from unrelated persons expressing DR4. This heterogeneity of DR4 was confirmed by mixed lymphocyte culture (MLC) experiments, indicating a close relationship between restriction epitopes and those that activate allogeneic T cells. Other clones seemed to be restricted by other class-II HLA determinants, most probably MT determinants of the T-cell donor. The restriction specificities were confirmed by subcloning experiments.

Effects of nonsteroidal antiinflammatory drugs on the immune network

The immune system is extremely complex. It comprises many different types of cells and their products. In patients with rheumatic diseases the immune system is activated and has disturbed regulation. It is also believed that immune reactions are involved in the pathogenesis of these disorders. Nonsteroidal antiinflammatory drugs (NSAID) have therapeutic effects on rheumatic diseases. These effects can all be explained by inhibition of prostaglandin production locally in the diseased joints, leading to reduced inflammation. Little or no effects on the number of circulating lymphocyte subpopulations or on peripheral blood mononuclear cell immune reactions can be seen after treatment of patients with rheumatoid arthritis (RA) with NSAID. The possibility, however, exists that immune reactions locally in the diseased joints are modulated by NSAID secondary to reduced prostaglandin production.

Different requirements for Ia-bearing accessory cells in mitogen versus antigen induction of human B-cell responses

The accessory cell requirements for the induction of proliferative and specific antibody responses of human lymphocytes stimulated with either antigen or mitogen were examined. An Ia-negative human myeloid tumor cell line, K562, could substitute for monocytes in the proliferation of monocyte-depleted lymphocytes in response to pokeweed mitogen (PWM) stimulation. K562 cells could also act as accessory cells in the PWM-induced anti-keyhole limpet hemocyanin (KLH) antibody synthesis of cells from a KLH-immunized donor. In contrast, only monocytes and not K562 cells could function as accessory cells in antigen-induced lymphocyte proliferation as well as in antigen-induced, antigen-specific antibody production. However, K562 cells, like monocytes, were able to positively and negatively regulate polyclonal immunoglobulin responses. Thus, Ia-bearing accessory cells can function in antigen-induced proliferation and antibody responses while non-Ia-bearing cells can function in mitogen-induced, but not antigen-induced responses. These studies indicate a dichotomy in the nature of required accessory cells in antigen-induced versus mitogen-induced human lymphocyte responses and strongly suggest an obligatory role of Ia or an Ia-related molecule on accessory cells in antigen-induced responses of human lymphocytes.

Human influenza virus-specific T helper cell clones can be restricted by MHC products different from serologically defined HLA-DR antigens

Clones of human influenza A virus-specific T lymphocytes were generated by limiting dilution after several in vitro stimulations with autologous influenza A/USSR virus-infected cells. The clones were expanded in T cell growth factor and then grown only in the presence of antigen and irradiated stimulator cells. The clones showed antigen specificity in that they were stimulated only by cells infected with influenza A virus, but not with influenza B virus; some clones even showed distinct reactivity patterns with several influenza A virus subtypes. All clones had the OKT3+4+8-phenotype. Analysis of the restriction elements for the recognition of viral antigens, demonstrated that most clones recognized antigens associated with but not identical to serologically defined HLA-DR specificities. From the recognition pattern with HLA-DR typed donors, three different restricting antigens could be demonstrated.

Unusual restriction of a proliferative line reacting with influenza A and B viruses

A human T-cell line, B3, has been obtained by cloning spleen cells at limiting dilutions in the presence of influenza-A-virus-infected autologous cells. B3 cells were OKT 3+4+8-, E rosetting+, Sig- and were HLA-DR (+) after stimulation and HLA-DR (-) when resting. They proliferate specifically in the presence of influenza-virus-infected cells. Remarkable is that (a) the proliferation was obtained with viruses of both A and B types and (b) only autologous cells seem to be able to present the viral antigen to B3 cells.

Both DR and MT class II HLA molecules may restrict proliferative T-lymphocyte responses to antigen

Antigen-primed T-cell blasts may be separated from alloreactive T cells on Percoll gradients. By means of this method, HLA restriction of antigen-specific proliferative T-cell responses may be studied, using allogeneic antigen-presenting cells carrying foreign D/DR antigens. The reported data confirm that the D/DR molecules as such are major restriction elements in the T-cell response to herpes simplex virus (HSV) and purified protein derivative (PPD). However, evidence is presented that other Class II HLA molecules, the MT molecules, may also function as restriction elements for the HSV response.

The role of HLA-DR antigens in PPD-stimulated lymphocyte-monocyte interactions

Autologous monocytes are required for an optimal lymphocyte proliferative response to purified protein derivate of tuberculin (PPD) in vitro and for a mixed lymphocyte culture induced by alloantigens. In the proliferative response to PPD we found that autologous monocytes could be replaced with HLA-DR-compatible monocytes and partly with HLA-DR semi-identical. In spite of a statistically significant difference between autologous and HLA-DR disparate monocytes in their cooperative capacity with PPD-stimulated lymphocytes, replacement in nearly one third of the cases was possible. These findings were supported by more detailed studies in which increasing numbers of allogenic and autologous monocytes were added to the isolated lymphocytes in the presence of PPD. It is concluded that the serologically defined HLA-DR antigens alone give insufficient information of the restriction elements controlling the PPD-stimulated lymphocyte-monocyte interactions.

HLA-D/DR restriction of proliferative T cell responses to antigen. Enrichment of antigen-specific T cell blasts and evidence of preferential HLA-D/DR restriction

Antigen-specific T cell blasts may be separated from alloreactive cells on Percoll gradients. The absence of alloreactivity allowed us to study HLA-D/DR restriction of proliferative T cell responses towards PPD and HSV antigens using allogeneic antigen-presenting cells. An overriding impact of self HLA-D/DR determinants as restriction elements for in vivo sensitized T cells was demonstrated. Furthermore, evidence was obtained that the proliferative PPD response might be preferentially restricted by HLA-D/DR 1.

Human T cell clones specific for tetanus toxoid: characterization of antigen specificity and HLA restriction

T cell blasts isolated from six-day cultures of peripheral blood mononuclear cells stimulated with tetanus toxoid (TT) were cloned in a two-layer agar system in the presence of autologous irradiated PBM (iPBM) and TT. Colonies were individually isolated and expanded in interleukin 2-containing medium. The antigen specificity of three T cell clones was attested by their capacity to proliferate under restimulation by TT and not by an unrelated antigen. The clones were specific for either the alpha or the beta chain of the toxin. T cells from these clones expressed Ia determinants and antigens of the helper/inducer T cell subset as defined by anti-T monoclonal antibodies. In the case of the alpha chain-specific clone MA 11 from the donor MA, allogeneic iPBM from HLA-compatible unrelated donors, including seven donors sharing one HLA DR specificity with MA, were found inefficient as antigen-presenting cells. A familial study, however, demonstrated that antigen presentation could be obtained using nonautologous cells. The presenting capability of cells from relatives of the donor MA segregated in association with the HLA-DRw6-bearing maternal haplotype present in MA. Results suggest that MA 11 cells recognized the antigen in the context of a surface determinant closely linked to HLA-DRw6.

Antigen-specific human T-lymphocyte clones. Genetic restriction of influenza virus-specific responses to HLA-D region genes

Human T lymphocytes, primed in vitro to influenza virus, were cloned by limiting dilution and expanded using medium containing interleukin 2 and feeder cells. A detailed analysis of the genetic requirements for induction of T-cell proliferation was conducted using a panel of cells from unrelated donors and two families who had previously been extensively phenotyped for HLA region antigens. Clones obtained from a Dw1, Dw3 individual required Dw1,DR1 histocompatibility for successful presentation of viral antigens by antigen-presenting cells. The antigen-presenting ability segregated with HLA-B,D,DR in an informative HLA-A/B recombinant individual. In contrast, some TLCs responded to antigen presented by cells that did not share known HLA antigens, and in one informative family, reactivity did not segregate with HLA. None of the T-cell clones reacted to allogeneic cells in the absence of antigen, suggesting that the TLCs do not bear receptors that recognize both influenza virus and alloantigen. In antibody-blocking studies, Dw1, DR1-restricted clones were blocked by all monoclonal anti-DR framework antibodies. The non-HLA-restricted TLCs were blocked by some, but not all, of the anti-DR framework monoclonal antibodies. These results confirm and extend the role of HLA-D region gene products in antigen presentation and also provide evidence that yet undefined cell interaction products, which may include hybrid structure, are able to participate in antigen-specific proliferative responses by human T cells.

Rheumatoid arthritis: a disease of T-lymphocyte/macrophage immunoregulation

In rheumatoid arthritis the synovial membrane has many of the characteristics of a hyperactive, immunologically-stimulated lymphoid organ. The basis of this hyperactivity is poorly understood. Highly specific antisera to human Ia-like (HLA-DR) antigens and monoclonal antibodies (OKT series) to various T-lymphocyte subsets were used to analyse both the normal and the rheumatoid synovium and to compare it with normal lymph nodes. In rheumatoid arthritis the synovium acquires an infiltrate with microanatomical similarities to the paracortical area of the lymph node. Large, very strongly HLA-DR-positive macrophage-like interdigitating cells form close contacts with the OKT4+ (inducer-type) T-cells, while the OKT8+ population (T-cells of suppressor-cytotoxic type) between the macrophage-OKT4+ cell clusters is scanty (T4/T8 ratio = 9:1). By contrast, in the lymph node there are more OKT8 T-cells interspersed between the HLA-DR+ interdigitating cells and OKT4+ cells (T4/T8 ratio = 2:1). The large interdigitating cells and the OKT4+ T-cell population may be mutually stimulatory. In the absence of efficient suppression this stimulation may lead to activation of B-lymphocytes and oligoclonal or polyclonal immunoglobulin synthesis, as is found in the synovial membrane in rheumatoid arthritis.

Studies on the role of HLA-DR in macrophage-T cell interactions

The purpose of this paper is to illustrate the difficulties we have encountered in attempting to analyse the role of HLA-DR in the antigen-dependent co-operation between macrophages and T cells which leads to a T-cell proliferative response. We have adopted the two most commonly used approaches; attempted inhibition by anti-HLA-DR antisera and study of co-operation between cells of unrelated individuals, and have found both methods unsatisfactory. With the first method we found that anti-HLA antisera could inhibit proliferative responses in a non-specific manner. Both anti-HLA-A, B and anti-HLA-DR antisera could inhibit and this inhibition was largely Fc-dependent. Using pepsin-digested antisera we have no evidence for a unique role for HLA-DR in these proliferative responses. The second method, study of co-operation between cells of unrelated individuals, proved extremely difficult to analyse because of the background allogeneic reaction. Whether cells of two individuals appeared to co-operate to give an antigen-specific response depended on the number of cells used and the calculations applied to the data. However, it was clearly possible to demonstrate co-operation between DR different individuals.