Genes on the X chromosome affect development of collagen-induced arthritis in mice

Susceptibility to collagen-induced arthritis (CIA) in mice is associated with a class II gene in MHC (Aq) but also with unknown genes outside MHC. Investigated here is the influence of genes on the X chromosome as well as the role of the X-linked immunodeficiency (xid) mutation. Reciprocal male F1 hybrids, bred to be heterozygous or homozygous for Aq, showed a genetic influence in their susceptibility to develop CIA. Crosses were made between B10.G, B10.Q, DBA/1, SWR/J, C3H.Q and CBA/Ca, and all F1 mice were castrated to avoid sex hormone modulation of the susceptibility. A differential timing of arthritis onset and severity were seen in the reciprocal F1 males. An exception was the reciprocal F1 male offspring from SWR/J and DBA/1 crosses which differed only in disease severity late in the course of the disease. The female F1 crosses did not show the same pattern of differential susceptibility to CIA as the F1 males. To exclude the possible influence of the Y chromosome, F1 males of reciprocal crosses were back-crossed to the parental strains creating offspring with equal X chromosomes but divergent Y chromosomes. No difference in development of arthritis was observed in these. The influence of the xid mutation was investigated next. The xid loci from the CBA/N mouse was bred into DBA/1 strain which is highly susceptible to CIA. The resulting congenic DBA/1-xid strain was resistant to induction of CIA and did not develop an antibody response to type II collagen. We conclude that polymorphic genes on the X chromosome modulate susceptibility to CIA. The results from the experiments with mice carrying xid mutations confirm that such immune modulating genes exist on the sex chromosomes.