Rat arthritis due to whole group B streptococci. Clinical and histopathologic features compared with groups A and D.

Heat-killed streptococci of Groups A, B, and D injected intraperitoneally into Sprague-Dawley rats induced arthritis. The histopathologic features of the arthritis were those of erosive synovitis. Early acute lesions were associated with deposits of streptococcal antigens. The serogroups and the physical state of the streptococci determined the incidence, the time of onset, the duration, and the severity of the disease, the severity being a blend of degree of inflammation, tendency to relapse, and occurrence of ankylosis. Whole Group A usually failed to induce arthritis. Group A disrupted with sonication regularly induced arthritis after a 24-hour latent period. The disease lasted over 60 days and caused ankylosis. Whole Group B regularly induced arthritis but only after a latent period of 6-8 days. The disease lasted over 40 days and caused ankylosed joints. With sonicated Group B a similar disease was induced, except that, as with sonicated Group A, the latent period was 24 hours. Whole Group D induced disease after a latent period of 48 hours. The arthritis lasted only 2 weeks and was transient. In contrast to its effects on Group A and B cocci, sonication of Group D abrogated its capacity to induce arthritis. It is postulated that for whole streptococci, in contrast to sonicated streptococci, arthritogenicity depends on the sensitivity of the cocci to initial processing in vivo. Processing may be partial digestion by enzymes of phagocytes. Cocci such as those of Group A that are insensitive to processing, injected whole, tend not to cause arthritis, but when they do cause disease, it is chronic. A coccus, such as one of Group D, that is very sensitive to processing produces a transient arthritis after a short latent period, while a coccus of intermediate sensitivity, such as one of Group B, induces disease only after a substantial latent period, and the disease is severe and chronic. The nature of processing remains to be determined.