Suppression of cytokine production by supernatants from CD8+ lymphocytes activated by mycobacterial fractions: The role of interleukins 4 and 6

Supernatants derived from CD8⁺ lymphocytes treated with mycobacterial components, or the partially purified carbohydrates from these supernatants, increased the production of IL-4 and IL-6 by mononuclear cells. The addition of anti-IL4 or anti-IL6 antibodies to LPS stimulated MN cells incubated with supernatants from CD8⁺ lymphocytes or carbohydrates resulted in the restoration of other cytokine production by these MN cells. Recombinant IL-4 and IL-6 on their own suppressed the production of IL-1, TNF-, IL-2 and IFN- by mononuclear cells. Such suppression could be reversed with antibodies to IL-4 and IL-6. The addition of rIL-4 and rIL-6 did not increase the suppression of cytokine production induced by suppressor supernatants or carbohydrates. Interleukin 4 decreased the production of IL-6 by MN cells; whilst IL-6 suppressed IL-4 production in a dose dependent manner. Both effects could be reversed with the appropriate antisera. Our results suggest that mycobacteria could evade host immunity by inducing the production of IL-4 and IL-6 by host mononuclear cells. These cytokines, in turn, would suppress the production of other cytokines necessary for effective cellular immunity.Abbreviations IL-1 interleukin 1 - IL-2 interleukin 2 - IL-4 interleukin 4 - IL-6 interleukin 6 - IFN- gamma interferon - TNF- tumour necrosis factor alpha - MN cells mononuclear cells - NAL's non-adherent lymphocytes - LPS lipopolysaccharide - PMA phorbol myristate acetate - RIA radioimmunoassay - ELISA enzyme-linked immunosorbent assay - rIL-4 recombinant interlukin-4 - rIL-6 recombinant interleukin-6 - U/ml units per millilitre - g/ml micrograms per millilitre - ng/ml nanograms per millilitre