Cross-reactivity of antibody responses to Borrelia afzelii OspC

The tick-transmitted bacterium Borrelia afzelii consists of a number of
antigenically different strains ¾ often defined by outer surface protein C
(OspC) genotype ¾ that coexist at stable frequencies in host populations.
To investigate how host antibody responses affect strain coexistence, we
measured antibody cross-reactivity to three different OspC types (OspC 2,
3 and 9) in three different strains of laboratory mice (BALB/c, C3H and
C57BL/6). The extent of cross-reactivity differed between mouse strains,
being higher in C3H than BALB/c and C57BL/6. In one of three pairwise
comparisons of OspC types (OspC2 vs OspC9), there was evidence for
asymmetry of cross-reactivity, with antibodies to OspC2 cross-reacting
more strongly with OspC9 than vice versa. These results indicate that the
extent of antibody-mediated competition between OspC types may depend on
the composition of the host population, and that such competition may be
asymmetric. We discuss the implications of these results for understanding
the coexistence of OspC types.