INDUCTION OF INTERLEUKIN-6 MESSENGER-RNA IN RAT ALVEOLAR MACROPHAGES BY IN-VITRO EXPOSURE TO BOTH CRYPTOCOCCUS-NEOFORMANS AND ANTI-C-NEOFORMANS ANTISERUM

Lewis rat alveolar macrophages (AM) were harvested and exposed in vitr o to Cryptococcus neoformans to investigate the induction of inflammat ory cytokines. AM in tissue culture wells were incubated with viable y east cells of C. neoformans or the capsular polysaccharide, glucuronox ylomannan (GXM), with or without rabbit anti-C. neoformans antiserum. At 3, 6, 12 and 24 h, AM were washed, lyzed and total RNA was isolated . Using reverse transcription-PCR, the transcripts of cytokine genes w ere semi-quantified by comparison with constitutive transcripts. Incub ation of AM with lipopolysaccharide, as positive control, induced elev ated levels of the three transcripts measured: interleukin (IL)-1a, IL -6 and tumour necrosis factor (TNF)-a. Under the same conditions,no ob vious changes were observed in the levels of transcription of these cy tokines by AM after exposure to several strains of C. neoformans. Howe ver, AM that were incubated with both the yeast cells and rabbit polyc lonal antisera to C. neoformans manifested significantly increased lev els of mRNA for IL-6, but not IL-la or TNF-a. This increased level of IL-6 mRNA was detectable after incubation for 6 or 12 h. Levels of tra nscription in AM were unaffected by exposure to normal rabbit serum, s pecific antiserum alone, GXM at concentrations of 10, 100 or 500 mu g ml(-1), or GXM and antiserum. Adsorption of the antiserum with heat-ki lled yeast cells of C. neoformans diminished its ability to induce IL- 6 mRNA in combination with fresh, viable yeast cells. The induction of IL-6 mRNA by yeast cells and antiserum does not require intact comple ment. In the absence of complement, the rabbit antiserum served as a p otent opsonin and markedly increased phagocytosis of C. neoformans by AM. These results indicate that antibody-opsonized C. neoformans are r eadily phagocytosed by rat AM, and that antibody-mediated phagocytosis may differ from complement-mediated phagocytosis in the subsequent st imulation of IL-6.