Differences in the immune response against ruminant chlamydial strains in a murine model

CBA/J mice were used in the present study to establish differences between the immune response to three chlamydial strains: AB7 (Chlamydia psittaci wi ld-type strain), 1B (C, psittaci vaccinal strain) and iB1 (C. pecorum). The evolution of chlamydial infection was evaluated in each strain by studying the clinical signs, the number of bacteria isolated from the spleen and th e pathology of the liver. Three aspects of the immune response were then st udied: the characterization of the infiltrate of leukocytes in the liver, t he percentages of T- and B-cells, macrophages and neutrophils in the spleen , and the presence of cytokines in the serum. Infection followed a differen t course in the C. psittaci-infected mice; 1B-infected mice showed milder l evels in all the parameters analysed than their AB7-infected counterparts. The resolution of infection was earlier in 1B-infected mice and, although t he immune response to both strains was Th1-like, a more intense CD8(+) T-ce ll response and an earlier presence of TNF-alpha in serum were observed in this group. C. pecorum infection was controlled mainly by a non-specific im mune response, since these mice showed no signs of a systemic specific immu ne response. Neutrophil depletion experiments showed that these cells play a very limited role in the non-specific response against C. pecorum. (C) In ra/Elsevier, Paris.