Characterization of background anti-trinitrophenyl plaque-forming cells observed in several strains of mice.

Normal mice have a large number of background anti-trinitrophenyl (TNP) antibody-forming cells (AFC) in their spleens (about 40-50 anti-TNP PFC/10(6) cells). We investigated this among several mouse strains, i.e., C57BL/6, C3H/He, Balb/c, ddd, and ICR mice, and found that all strains had a similar number of anti-TNP PFC (plaque-forming cells). Developmental aspects of background anti-TNP PFC in the ontogenic process were also investigated. The number of anti-TNP PFC increased logari thmically during the first few days of age, reached a peak on the 13th day and attained a constant value within 30 days. Neonatal thymectomy did not decrease the number of background anti-TNP PFC but such treatment decreased the anti-TNP PFC response to TNP-HRBC (horse red blood cells) immunization. Germ-free ICR mice had a number of background anti -TNP PFC similar to that of conventional ICR mice. Avidity of background anti-TNP PFC was compared among mice of several ages and it was shown that there were no differences among them. These results suggest that the occurrence of these background anti-TNP PFC is not elicited by the immune response but by the natural maturation of precursors of ACF without antigenic stimulation.