Responses of fractionated cells from patients with systemic lupus erythematosus and normals to plant mitogen: evidence for a suppressor population of monocytes

Decreased T cell response to anti-CD2 in systemic lupus erythematosus and reversal by anti-CD28: evidence for impaired T cell-accessory cell interaction

OBJECTIVE

To assess the ability of T cells from patients with systemic lupus erythematosus (SLE) to respond to a mitogenic combination of anti-CD2 monoclonal antibodies (MAb), and to learn the molecular basis of the documented defect.

METHODS

Peripheral blood mononuclear cell (PBMC) populations from individuals with SLE and paired controls were stimulated in vitro with anti-CD2, and the proliferative response was compared with that evoked by stimulation with phytohemagglutinin (PHA) and anti-CD3. Surface markers on lymphocyte populations were assessed by flow cytometry after staining with specific MAb.

RESULTS

The proliferative response to anti-CD2 was decreased to a greater extent than was the response to anti-CD3 or PHA in SLE patients. This defect was found in approximately one-half of the patients examined, was not associated with disease activity, and was maintained upon repeated testing. Since either monocytes or resting B cells can serve as accessory cells for T cells following activation by anti-CD2, we examined the T cell response after depletion of adherent cells. In approximately two-thirds of the individuals with a decreased response, depletion of monocytes or substitution of monocytes with allogeneic, resting B cells from normal donors corrected the defect. The addition to PBMC of anti-CD28, but not of a neutralizing antibody to interleukin-10, largely reversed the anti-CD2 proliferative defect. Significantly fewer CD8+ T cells expressed CD28 in SLE, and this defect was also documented, to a lesser extent, in CD4+ cells.

CONCLUSION

This study provides evidence that some functional T cell defects in SLE may be due, at least in part, to decreased CD28-mediated costimulatory activity following the interaction of T cells with conventional accessory cells.

Studies on the induction of anterior chamber-associated immune deviation (ACAID). III. Induction of ACAID depends upon intraocular transforming growth factor-beta

Delayed hypersensitivity (DH), the prototypical form of cell-mediated immune responsiveness, is mediated with the participation of considerable nonspecific inflammation which necessarily disrupts the anatomic integrity of involved and adjacent tissues. Damage of this type is of minor consequence to many visceral and cutaneous organs, but is of devastating consequence for organs such as the eye and the brain. At least in the case of the eye, the organ is remarkably adept at regulating the immune system's ability to respond to intraocular antigens by selectively down-regulating both the induction and expression of delayed hypersensitivity while leaving other effector modalities intact. This ability of the eye to selectivity down-regulate systemic DH responses to intracamerally inoculated antigens is known as anterior chamber-associated immune deviation (ACAID) and is mediated in part by antigen-specific regulatory T cells. Recent work suggests that macrophages (M phi) that reside in the iris and ciliary body can migrate out of an antigen-bearing eye and activate regulatory T cells within the spleen. In an effort to understand the mechanism by which intraocular M phi interact with antigen in the anterior chamber of the eye (AC) and subsequently induce splenic regulatory cells in ACAID, we have investigated what role, if any, the AC microenvironment itself plays in ACAID induction. The results reveal that CD45- parenchymal iris/ciliary cells secrete a soluble factor(s) locally and into the aqueous humor which endows resident, mature M phi with ACAID-inducing capabilities. Mice receiving infusions of these altered, antigen-pulsed M phi are incapable of mounting a significant DH response following immunization with antigen in adjuvant. Importantly, the ACAID-inducing effect is achieved when conventional, extraocular M phi are exposed in vitro to a soluble factor present in aqueous humor or culture SN from iris and ciliary body cells. Further investigations into the identity of this factor reveal it to be transforming growth factor-beta (TGF-beta). The role of TGF-beta in the generation of ACAID, as well as the implications of these findings to an understanding of immunologic privilege in general, are discussed.

Reduced function of HLA-DR-positive monocytes in patients with systemic lupus erythematosus (SLE)

Accessory function of monocytes for T-cell activation was studied in patients with systemic lupus erythematosus (SLE). Nylon column-purified T cells alone were not activated to proliferate by stimulation with concanavalin A (Con A), but the addition of dish-adherent monocytes restored the T-cell response in a dose-dependent manner (accessory function). This accessory function is mediated by HLA-DR-positive monocytes. This accessory function of monocytes was markedly impaired in SLE patients. The dysfunction of monocytes was marked in an active stage of SLE but not in an inactive stage of SLE. Furthermore, SLE T cells were not fully activated with Con A in the presence of normal monocytes, suggesting that both monocyte and T-cell functions were impaired in SLE patients. The dysfunction of SLE monocytes was due to neither the development of suppressor monocytes nor the overproduction of prostaglandins, because SLE monocytes did not suppress the accessory function of normal monocytes and indomethacin did not restore the dysfunction of SLE monocytes. The percentage of HLA-DR-positive cells in a monocyte population was markedly decreased in active SLE patients and moderately decreased in inactive SLE patients. Thus, the impairment of accessory function of monocytes in SLE patients seems to be derived from a decrease in HLA-DR-positive monocytes. These results suggest that the dysfunction of HLA-DR-positive monocytes plays an important role in the pathogenesis of SLE.

Impaired B cell proliferation by Staphylococcus aureus Cowan 1 in patients with systemic lupus erythematosus

We examined the proliferative response to Staphylococcus aureus Cowan 1 (SAC) by enriched peripheral blood B cells from patients with systemic lupus erythematosus (SLE). Responses of B cells from patients with active and inactive SLE were significantly lower than those of B cells from normal individuals. Hyporesponsiveness to SAC was not observed in healthy family members of SLE patients. This hyporesponsiveness did not correlate with prednisolone therapy and could not be attributed to serum factors; it did correlate with the presence of suppressor monocytes. However, we could not exclude the possibility of enhanced sensitivity of SLE B lymphocytes to suppressive signals delivered by the monocytes.

Immune dysfunction in diabetes-prone BB rats. Interleukin 2 production and other mitogen-induced responses are suppressed by activated macrophages

Spleen cells of diabetes-prone BB Wistar rats were found to generate excessively low proliferative responses, and interleukin 2 (IL-2) levels in response to T-dependent mitogens. This abnormality was not due solely to abnormal T cell numbers since: (a) addition of BB spleen cells of BB splenic macrophages to normal major histocompatibility complex (MHC)-matched Wistar Furth (WF) spleen cells resulted in severe suppression of concanavalin A (Con A)-, phytohemagglutinin (PHA)-, and pokeweed mitogen (PWM)-mediated proliferation, and IL-2 production; (b) macrophage depletion from BB spleen cells, but not B cell or T cell depletion, removed completely the suppressive effects of BB cells on WF cells; (c) macrophage depletion greatly enhanced the response of BB lymphocytes to T-dependent mitogens. Although suppressor macrophages could also be found in the spleen of WF control rats they were present in much smaller numbers than in the spleen of BB rats. The suppressive effect of BB macrophages was partially reduced by addition of the prostaglandin synthetase inhibitor indomethacin to cultures. Furthermore, indomethacin (but not catalase or PMA) considerably augmented IL-2 secretion of Con A-stimulated BB spleen cells, but had little effect on WF spleen cells. In contrast, prostaglandins E1 and E2 (PGE1 and PGE2) suppressed IL-2 production. While IL-2 secretion was severely depressed in BB rats unstimulated and lipopolysaccharide (LPS)-stimulated IL-1 secretion by splenic macrophages was normal. BB macrophages did not inactivate IL-2. Low IL-2 production and macrophage-mediated suppression were features of all BB rats tested.

Synovial fluid and blood monocytes/macrophages in rheumatoid arthritis. Influence on polyclonal activation of autologous B lymphocytes

The regulatory role of synovial fluid monocytes/macrophages from patients with rheumatoid arthritis in terms of B lymphocyte activation was evaluated by a reverse haemolytic plaque-forming cell (PFC) assay. Macrophage-depleted blood mononuclear cells (BMC) failed to respond to pokeweed mitogen (PWM). With autologous synovial fluid macrophages added, the PFC responses of macrophage-depleted BMC increased, and optimal concentration for full restoration of the PFC responses ranged from 8 to 35%. Synovial fluid mononuclear cells (SMC) as well as macrophage-depleted SMC were not able to respond to PWM. Addition of irradiated autologous blood macrophages to SMC did not increase the SMC PFC responses. It is concluded that the regulatory properties of synovial fluid macrophages do not explain the low PFC response of SMC to PWM.

Monocyte-induced inhibition of lymphocyte response to phytohaemagglutinin in progressive systemic sclerosis

In patients with progressive systemic sclerosis (PSS) lymphocyte responses to phytohaemagglutinin (PHA) are abnormal (27.2 +/- 3.5 X 10(-3) counts per minute (cpm) versus 69.8 +/- 4.4 X 10(-3) for normal persons, p less than 0.005). Removal of adherent peripheral blood mononuclear cells improves the response of PSS lymphocytes (42.3 +/- 3.4 X 10(-3) cpm, 155% of control) but diminishes the response of normal lymphocytes (60.3 +/- 5.9 +/- 10(-3), 86% of control). Supernatant fluids from cultures of PSS unfractionated and adherent cells depress normal T cell response to PHA (64% and 55% of control respectively), but supernatant fluids from normal unfractionated and adherent cells do not (104% and 101% of control). Supernatant fluids of PSS and normal adherent cells, cultured in the presence of indomethacin, are not inhibitory to normal T cells (109 +/- 15% and 124 +/- 14% of control respectively). Supernatant fluids from PSS patients are more inhibitory than comparable fluids from patients with systemic lupus erythematosus (60 +/- 8% of control versus 80 +/- 5% of control). These data support the hypothesis that cellular immunity is abnormal in patients with PSS and indicate that adherent mononuclear cells mediate at least one component of the abnormality via an indomethacin-sensitive mechanism.

Studies of autologous mixed lymphocyte reactions in patients with systemic lupus erythematosus

The autologous mixed lymphocyte reaction (AMLR) measures the proliferative response of peripheral blood T cells to surface antigens of non T cells. The AMLR of SLE patients with active or inactive disease either with (13) or without (6) immunosuppressive treatment was low compared with age and sex-matched controls, confirming previous reports. Only one patient with inactive, untreated SLE and one with drug induced lupus (procainamide) showed normal AMLR. Autologous reactivity was also reduced in 2 patients without treatment who presented with clinically complex disease syndromes, including primary biliary cirrhosis, or polyarteritis nodosa, together with Sjögren's syndrome and serological evidence of lupus. The AMLR could not be increased by changing the ratio of responder to stimulator cells. Patients with decreased AMLR also showed a decreased response to phytohemagglutinin which suggested a general depression of T cells. There was no correlation between the decreased AMLR and age, clinical features or anti-DNA antibody levels of the patients. In allogeneic mixed lymphocyte reactions (MLR) it was shown that non-T cells from SLE patients were poorer stimulators of allogeneic T cells than normal cells, and T lymphocytes from SLE patients were poorer responders to allogeneic non-T cells than were normal T cells. Both effects were much more marked in patients with active disease than in those with inactive SLE. This suggests a defect in both responder and stimulating cell populations in SLE.

Influence of autologous monocytes on the pokeweed mitogen-induced generation of immunoglobulin-secreting cells in man

The regulatory influence of autologous blood monocytes on the PWM-induced generation of Ig-secreting cells was assessed using a reverse haemolytic plaque forming cell (PFC) assay. The PWM-induced PFC responses of monocyte-depleted cells were low or absent in most cases. Addition of 12-42% freshly isolated monocytes fully reconstituted the IgM-, IgG- and IgA-PFC responses. With more monocytes added, the PFC responses declined. Monocytes precultured for 48 h supported the PFC responses of monocyte-depleted cells less well and addition of monocytes stimulated with phorbol myristate acetate (PMA) did not increase the response. The low responses of monocyte-depleted cells co-cultured with precultured monocytes were not increased by addition of supernatant from monocyte cultures. The PFC responses of mononuclear cells induced by PWM were significantly inhibited by unstimulated precultured monocytes, and to a larger degree by PMA-treated monocytes, indicating the presence of suppressor cells among the precultured monocytes. The PWM-induced thymidine incorporation by monocyte-depleted cells with precultured monocytes added was only slightly lower than that obtained with freshly isolated monocytes added, suggesting that the suppressive role of precultured monocytes was not due to cytotoxicity.

Stimulation of Immunoglobulin production from human B lymphocytes by Staphylococcus aureus: effects of monocytes and con A-induced suppressor cells

Significant immunoglobulin (Ig) production by human peripheral blood lymphocytes was induced in vitro by stimulating the cells with pokeweed mitogen (PWM) and Staphylococcus aureus Cowan I (SpA CoI). IgG, IgM, and IgA were determined by a combination of the latex fixation test and radioimmunoassay. High levels (1,000 to 5,000 microgram/ml of IgG and IgM and a lesser amount of IgA were constantly produced during 7 to 8 days of incubation with both stimulants. Ig production induced by SpA CoI stimulation was independent of the presence of T cells, while Ig production induced by PWM required T cells exclusively. Depletion of monocytes in the culture caused but a slight decrease in Ig production (particularly in the case of IgG). While the addition of a small number of monocytes enhanced IgG induction by both stimulants, coculture with an excess number of monocytes inhibited Ig induction (particularly IgG) by PWM stimulation but not by SpA CoI stimulation. Marked suppression of Ig production (IgG, IgM, and IgA) was observed in cocultures with Con A-activated T cells. The phenomena of suppression were observed in both the SpA CoI-stimulated and PWM-stimulated lymphocytes. These data indicated that Ig production from B cells and relatively of independent of monocytes, but could be subjected to the regulation of the Con A-induced suppressor T cells.

Impaired antigen-specific suppressor cell activity in patients with rheumatoid arthritis

Antigen-specific suppressor cell activity of peripheral blood mononuclear cells was investigated in 20 patients with rheumatoid arthritis (RA) and 16 age- and sex-matched healthy controls. Suppressor cell activity was generated by priming peripheral blood mononuclear cells with high dose antigen (ovalbumin) and adding the washed primed or control (unprimed) cells to autologous, optimally stimulated, target plaque forming cell (PFC) cultures. The ability of the primed cells to interfere with an optimal ovalbumin specific PFC response in the target culture was used as a measure of antigen-specific suppressor cell activity. The results demonstrated that the mean (+/- SE) PFC response of the rheumatoid patients (669 +/- 76 PFC/10(6) cells) was not statistically different from that of the normal controls (722 +/- 83 PFC/10(6) cells), P = 0.1. However, reduced suppressor cell activity was observed in the rheumatoid patients relative to controls (46.4 +/- 4.2% versus 64.6 +/- 2.7% suppression, respectively; P < 0.001). No correlation was demonstrated between suppressor cell activity in rheumatoid patients and disease activity or therapy.

Suppressor monocytes in human disease: a review

Suppressor monocytes have been found in a number of human diseases most of which are associated with lymphopenia and deficiences in cell mediated immunity. In our studies both quantitative and qualitative differences in monocytes were detected in certain patients with advanced Hodgkin's disease or tuberculosis. In certain patients lymphocyte activating factor production by monocytes was severely depressed in part secondary to decreased activation by suppressed T cells, although at times primary impairment of macrophage function was also probably contributory. Mononuclear cell cultures from patients with advanced Hodgkin's disease also manifested excessive prostaglandin secretion; however, the association of this with monocyte suppression and deficient LAF production was inconstant. Furthermore, reversibility of monocyte suppression could not regularly be achieved by inhibition of prostaglandin synthetase with indomethacin suggesting that excessive production of prostaglandins is unlikely to be the sole mechanism of monocyte inhibition of lymphoproliferation. It also remains to be established whether the inhibition of lymphoproliferation in vitro is important to in vivo delayed hypersensitivity or whether the mechanism is related to other macrophage effects such as tumor cytostasis and cytolysis.