TRANSFORMING GROWTH FACTOR-BETA(1) (TGF-BETA(1) CONTROLS EXPRESSION OF MAJOR HISTOCOMPATIBILITY GENES IN THE POSTNATAL MOUSE - ABERRANT HISTOCOMPATIBILITY ANTIGEN EXPRESSION IN THE PATHOGENESIS OF THE TGF-BETA(1) NULL MOUSE PHENOTYPE

The phenotype of the transforming growth factor beta1 (TGF-beta1) null mouse has been previously described and is characterized by inflammatory infiltrates in multiple organs leading to a wasting syndrome and death as early as 3 weeks after birth. Since this phenotype occurs in the absence of any detectable pathogen, potential autoimmune disease mechanisms were investigated. We examined major histocompatibility complex (MHC) mRNA expression in tissues of the TGF-beta1 null mouse and found levels of both the class I and class II MHC mRNA elevated compared to normal or TGF-beta1 heterozygous littermates. This elevated expression was seen prior to any evidence of inflammatory infiltrates, suggesting a causal relationship between increased MHC expression and activation of immune cell populations. Cell surface expression of MHC molecules was detected by immunohistochemistry and correlated well with mRNA levels. Expression of mRNA for interferon gamma and its receptor was unchanged at the ages when increased MHC expression became apparent. Down-regulation of class I MHC expression by TGF-beta1 was also demonstrated in vitro in fibroblasts isolated from TGF-beta1 null mice. These findings suggest that one natural function of TGF-beta1 is to control expression of both MHC classes. Altered regulation of MHC expression may be a critical step leading to the multifocal inflammation and wasting syndrome seen in the TGF-beta1 null mouse. These results suggest potential applications for TGF-beta in the management of autoimmune disease, allograft rejection, and other problems associated with altered MHC expression.