Effects of salicylates on blood changes in mycoplasma arthritis in rats.

1. The polyarthritis produced in rats by i.v. inoculation with Mycoplasma arthritidis was made more severe by salicylates.2. The infection increased the erythrocyte sedimentation rate (ESR), serum lysozyme, counts of total white blood corpuscles, polymorphonuclear cells and lymphocytes, haemolytic serum complement (CH 50) and its component C3. Salicylates enhanced the rise in ESR, CH 50 and C3, but suppressed the rise in lymphocytes and even induced a fall.3. Salicylates did not interfere with the development and action of metabolic inhibition antibodies against M. arthritidis, and did not promote the growth of M. arthritidis.4. Rats treated with salicylate during the first infection acquired the same immunity to reinfection as did infected controls.5. Salicylates did not render rats susceptible to M. fermentans which is non-pathogenic to rats, but may be involved in human rheumatoid arthritis.