Cytokine-mediated inhibition of erythropoietin synthesis by dexamethasone.

The effect of inflammatory cytokines on the in-vitro synthesis of erythropoietin by HepG2 cells was evaluated. Monocyte-conditioned medium, and the cytokines interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha all reduced synthesis of erythropoietin. The steroidal anti-inflammatory drug, dexamethasone, did not affect cytokine-mediated erythropoietin inhibition. Dexamethasone did cause a reduction in the secretion of erythropoietin inhibitory cytokines from monocytes. These results point to a possible therapeutic approach in the treatment of anaemia caused by suppression of erythropoietin synthesis by monocytic cytokines.

Cellular immunity in tuberculous pleural effusions: evidence of spontaneous lymphocyte proliferation and antigen-specific accelerated responses to purified protein derivative (PPD).

The kinetics of in vitro cellular proliferation against a PPD of Mycobacterium tuberculosis or streptococcal antigen (streptokinase-streptodornase) was evaluated in pleural fluid and peripheral blood mononuclear cells (PBMC) from patients with tuberculous and non-tuberculous pleuritis. The peak proliferative response to PPD by mononuclear cells from pleural fluid occurred earlier (day 3) in 65% of patients with tuberculosis, a finding not seen in non-tuberculous effusions. Spontaneous lymphocyte proliferation of both peripheral blood lymphocytes and pleural effusion lymphocytes was frequently observed, irrespective of etiology. However, 20 of 21 tuberculous patients manifesting spontaneous lymphocyte proliferation had accelerated kinetics of proliferation to PPD, which was antigen-specific. These results suggest that spontaneous lymphocyte proliferation occurs as a response to antigen stimulation at the site of disease, and is not a non-specific response to inflammation. Furthermore, enhanced reactivity against mycobacterial antigen, manifested by accelerated kinetics of proliferation, has diagnostic potential in patients with pleural effusions.

Evidence for in vivo generation of cytotoxic T cells. PPD-stimulated lymphocytes from tuberculous pleural effusions demonstrate enhanced cytotoxicity with accelerated kinetics of induction.

Mycobacterium tuberculosis is a bacterial pathogen capable of survival and replication within human macrophages. Cytotoxic T cells are thought to be important for the eradication of infected macrophages. To test this hypothesis, pleural effusion lymphocytes from patients with tuberculous pleuritis were stimulated in vitro with PPD, and proliferation and cytotoxicity were assessed by thymidine incorporation and chromium release, respectively. The level and kinetics of generation of antigen-specific cytotoxicity were measured and compared with those in autologous peripheral blood, control peripheral blood, and nontuberculous effusions. Both proliferation and cytotoxicity in tuberculous pleural effusions were augmented and accelerated in comparison to autologous or control peripheral blood. By contrast, low levels of cytotoxicity were observed in nontuberculous effusions, without evidence of accelerated kinetics. Cell subset fractionation by panning indicated that the cytotoxicity was mediated by CD4+ cells. The accelerated kinetics of induction of PPD-specific cytotoxic T cells demonstrated here suggests reactivation of in vivo generated cytotoxic T cells. These findings provide evidence that cytotoxic T cells are induced at the site of pathology in vivo and suggest that these cells play an important role in protection in vivo against infection with tuberculosis.

Compartmentalization of the cellular immune response to the recombinant 65 kDa protein of Mycobacterium bovis BCG in patients with tuberculous pleuritis.

The recombinant 65 kDa mycobacterial protein of M. bovis BCG has been shown to be immunodominant in mice immunized with M. tuberculosis. Little is known about reactivity to this antigen in patients with tuberculous pleuritis. In this study therefore, pleural effusion and autologous peripheral blood lymphocytes obtained from patients with tuberculous and nontuberculous pleuritis were stimulated in-vitro with the recombinant 65 kDa antigen. Proliferation was assessed by 3[H] thymidine incorporation. In addition, pleural effusion lymphocytes were activated in vitro with the 65 kDa antigen and tested for cytotoxic activity in 15-hr chromium-release assays. Pleural effusion lymphocytes obtained from a high percentage (56%) of patients with tuberculous pleuritis showed significant proliferative responses to the 65 kDa antigen, while the response in autologous peripheral blood lymphocytes was significantly lower. By contrast, pleural effusion lymphocytes obtained from patients with nontuberculous effusions were not reactive to the 65 kDa antigen. In addition, 65 kDa stimulated pleural effusion lymphocytes obtained from patients with tuberculous effusions showed antigen-specific lysis of autologous targets pulsed with the 65 kDa antigen. These results indicate compartmentalization of the immune response to the 65 kDa antigen and, in addition, provide evidence for in vivo involvement of this antigen in the immune response to M. tuberculosis.