DISTINCT CHARACTERISTICS OF RESISTANCE TO BORRELIA-BURGDORFERI INDUCED ARTHRITIS IN C57BL 6N MICE/

Studies of mice infected with Borrelia burgdorferi have indicated that the severity of arthritis is influenced by the genetic composition of the host: the C3H mouse develops severe arthritis while BALB/c and C5 7BL/6 mice develop mild arthritis. In this study, the effects of incre asing infectious dose on the severity of arthritis were determined in these three mouse strains. C3H/He mice developed severe arthritis at a ll infectious doses, with 100% infection requiring 200 spirochetes. In BALB/cAnN mice, arthritis severity was dependent on infectious dose; symptoms were mild with infection by 200 B. burgdorferi and progressiv ely more severe with increasing infectious dose. Infection of BALB/cAn N mice with 2 x 10(4) B. burgdorferi resulted in arthritis with severi ty identical to that in C3H/He mice. Spirochete levels in rear ankle j oints of C3H/HeJ and C3H/HeN mice were relatively high, as detected by PCR, and did not increase with infectious dose. Spirochete levels in joints from BALB/cAnN mice increased,vith increasing infectious dose t o levels found in severely arthritic C3H/He mice. Thus, resistance to severe arthritis in BALB/cAnN mice was conditional: it could be overco me by high infectious dose and the arthritis became severe when high l evels of B. burgdorferi were present in joints. A unique response to i ncreasing infectious dose was seen in C57BL/6N mice, which displayed m ild to moderate arthritis at all doses of B. burgdorferi tested, up to 2 x 10(5). At all infectious doses, the levels of spirochetes in ankl e joints of C57BL/6N mice were high, equivalent to those found in the severely arthritic C3H/He mice. The arthritis observed in infected (C5 7BL/6N x C3H/HeN)F-1 mice was of severity intermediate between those o f the two parental strains. The finding that resistance to severe arth ritis in C57BL/6N mice could not be overcome by high infectious doses and was independent of spirochete levels in joints suggested that it w as mediated by a distinct mechanism from that operating in BALB/cAnN m ice.