The autologous mixed lymphocyte reaction. A precautionary note

Synovial fluid antigen-presenting cell function in rheumatoid arthritis

We have previously demonstrated enhanced synovial fluid (SF) antigen-presenting cell (APC) function in inflammatory arthritis patients selected on the basis of marked SF mononuclear cell (MNC) responsiveness to reactive arthritis-associated bacteria (Clin Exp Immunol 1990; 79:189-94). In this study we have assessed whether similarly enhanced synovial APC function is present in other inflammatory arthritis patients by using two assay systems to study 18 rheumatoid arthritis patients whose MNC responsiveness had not been determined in advance. We demonstrate that rheumatoid SF APC are much more potent than peripheral blood (PB) APC in stimulating the responses of autologous PB T cells to a range of recall antigens. In addition, SF APC are shown to be efficient stimulators of the antigen-specific responses of MHC-compatible, cloned T cells. Enhanced synovial APC function is thus likely to be a general feature of inflammatory arthritis and may play an important role in its pathogenesis.

Abnormalities in autologous mixed lymphocyte reaction-activated immunologic processes in systemic lupus erythematosus and their possible correction by interleukin 2

The autologous mixed lymphocyte reaction (AMLR) represents the activation, proliferation and differentiation of T cells in response to signals from autologous non-T cells. Upon stimulation by autologous non-T cells, OKT4+ cells produce interleukin 2 (IL2); cells contained within both OKT4+ and OKT8+ cell populations can also be activated by autologous non-T cells to become sensitive to IL2. Once these activated OKT4+ and OKT8+ cells are exposed to IL2 produced by OKT4+ cells, they will proliferate and go on to differentiate into effector cells. Patients with systemic lupus erythematosus (SLE) have a defect in the AMLR. The ability of OKT4+ cells to produce IL2 in the AMLR is impaired. Upon triggering with autologous non-T cells, their OKT8+ cells become sensitive to proliferative signals of IL2; however, their OKT4+ cells fail to express IL2 receptors. These defects are a consistent feature in patients with SLE. AMLR-induced immunologic processes which require cell interactions between OKT4+ cell subpopulations are not correctable even by the addition of normal IL2. However, the immunologic processes mediated through OKT4+-OKT8+ cell interactions can be corrected with normal IL2. The latter finding suggests that the partial correction of the AMLR-induced immunologic processes with IL2 might lead to suppressed B cell hyperactivity of patients with SLE.

The role of xenoantigen in the human autologous mixed lymphocyte reaction: ability to respond in the absence of exposure to xenoantigen depends on the method of T-cell preparation

Recent reports have suggested that the autologous mixed lymphocyte reaction (AMLR) is attributable to contaminating xenoantigen. T-cell populations separated from peripheral blood mononuclear cells (PBM) over Percoll fail to produce an AMLR in the absence of xenoantigen. However, T-cell populations that do not adhere to plastic and to nylon wool will in the absence of added xenoantigen produce an AMLR comparable to that obtained with E-rosetted populations. In the nonadherent cells separated sequentially by passage through nylon wool and Percoll, the presence of two lymphocyte subpopulations was demonstrated. One is xenoantigen dependent, the other xenoantigen independent in the AMLR. Further, the xenoantigen-independent population may provide help to the dependent population. In the previous reports with Percoll-separated cells that attributed the AMLR to contaminating xenoantigen, the xenoantigen-independent T-cell population was excluded from the responding fraction.

Monoclonal antibody analysis of responder and stimulator cells in the human autologous mixed lymphocyte reaction

Responder and stimulator cell subpopulations in the autologous mixed lymphocyte reaction (AMLR) were determined with the OK series of monoclonal antibodies. Mitomycin-C-treated, monocyte-enriched cell populations were used as stimulator cells in the AMLR. Treatment of these monocytes with either OKM and/or OKI monoclonal antibodies and complement resulted in a marked loss of ability of these cells to act as stimulators in the AMLR. Removal of OKT3+ and OKT4+ cells diminished the proliferative responses of AMLR cultures. Interaction of T cells with autologous monocytes resulted in generation of cells capable of suppressing both MLR and AMLR cultures. The suppressor activity of these cells was diminished by treatment with OKI , OKT4 or OKT8 monoclonal antibodies. No cytotoxic activity to autologous or allogeneic monocytes was observed. Additional studies showed an increased number of OKT9 + and OKI + as well as OKT8+ T cells in the AMLR responder cell population. This study indicates that cultures of T lymphocytes with autologous monocytes yield T cell subset(s) which suppress MLR and AMLR reactivity.

Role of autorosette forming cells in antibody synthesis in vitro: suppressive activity of ARFC in humoral immune response

The role of autologous rosette forming cells (ARFC) in humoral immune responses was studied using an in vitro system. While depletion of ARFCs from PBL resulted in a significant increase of either total IgG or anti-TT IgG, addition of these cells to the system decreased the production of immunoglobulin to a level comparable to that of unfractionated PBL. The majority of the ARFCs reacted with anti-Leu2a and anti-Leu8. In contrast, the majority of non-ARFCs reacted with Leu3a and only 10% with Leu8 monoclonal antibodies. Stimulation of unfractionated PBL with concanavalin A (ConA) resulted in an increase of the ARFC population. ConA stimulation also increased the number of cells reactive with anti-Leu2 and/or anti-Leu8. The autorosette population had a higher purine nucleoside phosphorylase (PNP) content than the non-ARFC population. Although the ARFC suppressed synthesis of antibody by B cell in vitro when they were mixed with either autologous or allogeneic B cells, a marked proliferation of non-B cells was evident. We conclude that at least two different subpopulations of T cells are capable of forming rosettes with autologous red blood cells.

The autologous mixed lymphocyte reaction is not primarily due to xenoantigenic stimulation

Autologous mixed lymphocyte reaction (AMLR) is an interesting in vitro system in which T lymphocytes proliferate when cultured with non-T cells from the same individual. Because this system has both memory and specificity and elicits help, suppression, cytotoxicity, and soluble mediators, it has been proposed that it reflects in vitro the complex interactions of the immunologic network as it operates in vivo. A recent study, however, has cast doubt on the significance of this reaction by implicating xenoantigens, present during separation and/or culture procedures (e.g., sheep red blood cells or fetal calf serum), in the proliferative response of T cells. This question is analyzed by performing AMLR studies with cells (from eight normal subjects) that were separated with and without the use of sheep erythrocytes, and incubated with either fetal calf serum on normal human AB serum. Results were similar in all circumstances and negate a primary role of xenoantigens in AMLR.

Autologous mixed lymphocyte reaction in health and disease states in man

In this review are discussed the nature of T cell subsets, defined with monoclonal antibodies, responding in T-non-T and T-T autologous mixed-lymphocyte reactions (AMLR) and antigens stimulating in AMLR, soluble products of AMLR and generation of suppressor, helper and cytotoxic functions. On the basis of these data a model of immunoregulation in vivo can be proposed. We believe that AMLR is a real-phenomenon and not an artefact and perhaps represents a mechanism by which various immune functions are regulated, including feedback regulation of AMLR. The significance of AMLR is further supported by studies in various human and animal diseases.