Somatic cell hybrids between macrophages from Bcgr and Bcgs mice: characterization of MHC class II expression

In order to gain a better understanding of the regulation of MHC class II expression related to the Bcg gene, we have produced macrophage-macrophage somatic cell hybrids by fusing the RAW 309 macrophage cell line derived from BALB/c.Bcgs mice with peritoneal macrophages from Bcgr C3H/HeN mice. The differential screening of the hybrids was based on the differential sensitivity of Ia expression to suppression with cycloheximide. We found that most of the hybrids expressed Ia without further stimulation with rIFN-gamma. Cycloheximide suppressed the expression of Ia by some of the hybrids. Treatment of these cells with rIFN-gamma resulted in a cycloheximide resistant Ia expression of both parental haplotypes. The macrophage hybrids produced IL-1 beta, IL-1 alpha, and TNF-alpha when stimulated with LPS. There was no correlation between the levels of monokines produced and the persistence of Ia expression. The results of this investigation indicate that the product of the Bcg gene contributed by macrophages from C3H/HeN mice will affect the expression of the I-Ad glycoprotein that is normally transiently expressed by the RAW 309 cell line.