Characterization of the induction of persistence of major histocompatibility complex class II by hybrids of macrophages from bacillus Calmette Guerin-resistant mice.

Peritoneal macrophages (M phi) from mice that are resistant to infection by Mycobacterium bovis (strain BCG) (Bcgr) can be induced to express major histocompatibility complex (MHC) class II glycoproteins (I-A) continuously upon treatment with 100 units of recombinant interferon-gamma (rIFN-gamma). In contrast, M phi from mice that are susceptible to BCG (Bcgs) express I-A transiently. Persistent expression of I-A does not require the continued synthesis of the glycoprotein. Thus, treatment with cycloheximide (CHX) reduces I-A expression by M phi that express I-A transiently but does not affect the expression of I-A that is persistently expressed. It was not possible, in these studies, to characterize the induction of persistence independent of MHC class II expression because of the 24-48 h required for MHC class II synthesis and cycling to the cell surface. During this time, persistence was also induced. To characterize persistence independent of MHC class II induction we have produced M phi-M phi somatic cell hybrids that express I-A constitutively by fusing cells from a Bcgs M phi cell line with M phi from Bcgr mice. Treatment of some of the hybrids with CHX reduced MHC class II expression. The M phi hybrids required treatment with high doses of rIFN-gamma to induce CHX-resistant I-A expression. The induction of the persistence of I-A, following the addition of rIFN-gamma, required a short burst of protein synthesis as well as the presence of rIFN-gamma for at least 3 h. The addition of actinomycin D simultaneously with rIFN-gamma did not prevent the induction of the persistence of I-A expression by one of the M phi hybrids (F6.4). In contrast, the induction of persistence of I-A expression required a longer period of induction than was observed for hybrid F6.4, which was attributed to the requirement for new RNA and protein synthesis by the A1.8 hybridoma.