Enhanced inhibition of lymphocyte activation by Mycobacterium avium complex in human T lymphotrophic virus type I carriers.

BACKGROUND: We have previously reported that disseminated pulmonary Mycobacterium avium complex (MAC) infection is more common in human T lymphotrophic virus type I (HTLV-I) carriers than in non-carriers. However, the reason for this remains unclear. It has been shown that glycopeptidelipid (GPL), one of the lipid components of the cell envelope of MAC, is able to reduce the lymphocyte blastogenic response to mitogens. The purpose of this study was to clarify whether or not the inhibitory effect of GPL differs between HTLV-I carriers and non-carriers.
METHODS: Peripheral blood lymphocytes were obtained from 29 patients who had recovered from pulmonary MAC infection (10 of whom also had HTLV-I infection) and the lymphocyte counts and T cell subpopulations of the peripheral blood lymphocytes in HTLV-I carriers and non-carriers were compared. The inhibitory effect of GPL on the lymphocyte blastogenic response to phytohaemagglutinin (PHA) was tested in these 29 cases and in 15 healthy controls who had never suffered from MAC (seven of whom also had HTLV-I infection). All HTLV-I positive cases were carriers.
RESULTS: There was no significant difference in the numbers or subset proportions of T cells between HTLV-I carriers and non-carriers. Lymphocyte activation by PHA was significantly inhibited by GPL in MAC positive and negative HTLV-I carriers compared with MAC negative non-carriers and MAC negative healthy controls (p<0.001).
CONCLUSIONS: We suggest that MAC infection leads to strong inhibition of lymphocyte activation in HTLV-I carriers. This may account, in part, for the severity of pulmonary MAC infection in HTLV-I carriers.