T cell-replacing factor for glucocorticosteroid-induced immunoglobulin production. A unique steroid-dependent cytokine.

Glucocorticosteroids (GCS) added to otherwise unstimulated cultures of human peripheral blood mononuclear cells (PBMC) induce the synthesis and secretion of all classes of immunoglobulin. The magnitude of this response is similar to that seen with other polyclonal B cell activators such as pokeweed mitogen (PWM), and like that of PWM, the steroid effect is dependent on both T cells and monocytes. To determine the cellular target for GCS in these cultures, separated populations of T cells and non-T cells were preincubated with steroids and then recombined. No immunoglobulin was produced in any of these preincubation experiments. As a different approach to this question, supernatants were collected from various cell populations following stimulation with PWM, concanavalin A (Con A), phytohemagglutinin (PHA), alloantigens, or GCS. These supernatants were tested for their effects on GCS-induced Ig production by B cells. Supernatants from 3-d cultures of unstimulated, as well as GCS-treated, PBMC contained a T cell-replacing factor that permitted T-depleted PBMC to produce Ig upon steroid stimulation. This supernatant factor (TRF-S) could be produced in the absence of steroid stimulation, but both the factor and GCS were necessary for the induction of Ig synthesis. Production of the TRF-S required the presence of both T cells and adherent cells in culture and was found in the highest concentrations at 3-4 d of culture. Supernatants from cultures stimulated with PWM, PHA, Con A, and alloantigens did not contain detectable TRF-S activity, and TRF-S was unable to replace helper T cells for PWM-induced Ig production. TRF-S required the presence of adherent cells in the T cell-depleted responder population for its action. Further, it was effective in inducing Ig production along with GCS in the presence of a sufficient concentration of cyclosporin A to block all T cell helper activity for primary responses of PBMC to PWM or GCS. TRF-S was inactivated by trypsin treatment, heating to 56 degrees C, freezing, lyophilization, and storage at 4 degrees C for greater than 3 wk. Its molecular weight is probably 10,000 daltons or more, since TRF-S activity is not rapidly dialyzable. These experiments indicate that GCS-induced Ig production by human B cells does not require the presence of intact T cells in the cultures and therefore the steroids are not exerting their influence directly on T suppressor or T helper cells. Furthermore, they demonstrate a previously unrecognized cytokine that induces the differentiation of human B cells to Ig production in the presence of GCS.

Abnormally elevated frequency of Epstein-Barr virus-infected B cells in the blood of patients with rheumatoid arthritis.

Patients with rheumatoid arthritis (RA) are known to have in vitro regulatory T cell abnormalities relating to Epstein-Barr virus (EBV). In this report, we asked whether patients with RA have more circulating EBV-infected B cells than normals. To address this question, we determined the frequency of spontaneously transforming B cells in the peripheral blood of 18 normals, 15 patients with RA, and 8 patients with systemic lupus erythematosus (SLE). The mean frequency of spontaneously transforming B cells in RA patients was 10.1/10(6) B cells, which was significantly greater than that of the normal controls, 2.8/10(6) B cells (P less than 0.005). The group of patients with SLE did not differ from the normals (P greater than 0.4). In further studies undertaken to investigate as to whether RA B cells are more easily transformed by EBV than normal B cells, we determined that the frequencies of transforming B cells in the presence of exogenous EBV were similar in RA patients and normals. Lymphocytes obtained from patients with RA demonstrate a profound T cell defect in their EBV-specific suppression, as measured in vitro; there was no direct correlation, however, between this in vitro T cell abnormality and the number of circulating EBV-infected B cells. Thus, patients with RA, as a group, have abnormally elevated numbers of circulating EBV-infected B cells, and this abnormality most likely derives from a complex dysregulation of the defense mechanisms for infection with EBV.

Glucocorticosteroids stimulate polyclonal immunoglobulin production by cord blood mononuclear cells.

Glucocorticosteroids (GCS) are in vitro polyclonal activators of immunoglobulin (Ig) production for human mononuclear cells (MC) from virtually all adult donors. However, GCS treatment of cord blood MC resulted in Ig production in only 12/41 samples. This GCS effect is T cell and monocyte dependent and is mediated in part by a soluble T cell replacing factor. The inconsistent response of cord MC could be due to either cellular or soluble factor differences from adults. In 11/12 samples tested, irradiated cord T cells did help adult B cells, but less than did irradiated allogeneic adult T cells. T cell suppression in cord samples is unlikely inasmuch as higher cord T cell numbers and proportions increased the number of responding cord samples. Cord monocytes function adequately, because monocytes supported GCS responses when cord non-T cells had sufficient T cell help. The T cell replacing factor was found in supernatants of unstimulated cord as well as in adult MC cultures, but was less than 50% as potent. Cord B cells did not develop GCS-induced Ig production with such supernatants, suggesting that cord B cells may require a higher concentration or more prolonged exposure to T cell help. With a 2:1 ratio of irradiated adult T cells to cord non-T cells, only 25% of cord samples responded to GCS (compared to greater than 95% of adult samples), but with a ratio of 4:1, 75% responded. IgM was the predominant isotype secreted by GCS-stimulated cord cells, but 6/14 samples also produced IgG and 8/14 produced IgA. Thus, the functional immaturity of both cord T and B cells exists for GCS-induced Ig production, but with appropriate conditions GCS can activate most samples of cord B cells to synthesize Ig.