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The pathogenicity for rat of M. arthritidis strain Jasmin and strain 20-P from rheumatoid synovial tissue were studied. Only strain Jasmin produced signs of illness in four of the 12 rats infected. A mycoplasma was isolated from three tissue specimens. Ten of the 48 rats investigated showed mycoplasma antibodies. Five rats showed minor inflammatory changes in the distal joints of the limbs. The failure to induce arthritic symptoms in rats inoculated with strain 20-P from rheumatoid arthritis may be due to its 10-year long storage outside the animal host.

Sera of 100 patients under examination at the Outpatient Department of the Rheumatism Foundation Hospital were studied by the indirect hemagglutination technique, using both mycoplasma reference strains, and isolates from RA and SLE as antigens. The series consisted of five groups: I, definite RA (49 patients); II, probable RA (11); III, possible RA or nonspecific inflammatory arthritis (34); IV, osteoarthrosis (2); V, Reiter's disease (4). Mycoplasma antibodies in titres of 16 or higher were encountered in groups I-IV in 26, 8, 19, and one case respectively. Twenty-one out of 106 blood donors had antibodies against an isolate from RA and/or M. arthritidis strain PG 6. The titres found were 16 or 32, except in two cases, 128. In the definite RA group, 21 out of 26 patients possessing mycoplasma antibodies, showed titres of 16 or higher against isolates from RA and/or SLE, 12 against M. arthritidis strain PG 6 and/or Campo, 8 against M. fermentans, and 6 against a T-strain from NGU. Antibodies against M. arthritidis strain Campo were found more often than against strain PG 6. The longer the duration of the arthritic symptoms was, the more frequent seemed also to be the occurrence of mycoplasma antibodies.

Using a modified cell-free culture medium and modern microscopic equipment, a mycoplasma was isolated from scrapings of skin lesions of three patients with lepromatous leprosy. Three specimens were taken from the first patients. All five isolates were arginine-positive and their antibiotic sensitivity was identical with only one slight exception.