A large number of hybridomas were constructed by fusion of B cells from perinatal liver and spleen. Many of these showed multispecificity, high interconnectivity and anti‐idiotype (Id) activity. Several of these were subjected to a detailed analysis to evaluate their influence on the developing immune system. A hybridoma BD2 (μ,χ), derived from 2‐day‐old liver, was shown to have anti‐T15 and anti‐J558 activity by inhibition enzyme‐linked immunosorbent assay and by in vivo administration. BD2 reduced primary T15 and J558 Id in adult BALB/c by 50%. In contrast, timed administration of this antibody during neonatal periods resulted in enhancement of responses to phosphorylcholine (PC) and a(l ‐>3)‐linked dextran (Dex) when these mice were challenged as adults. Another hybridoma DB3 (μ,χ), derived from a lipopolysaccharide‐stimulated fetal liver, reacts with GB4–10 (anti‐ T15) and not with PC. It also reacts with BD2. It is thus anti‐anti‐Id with respect to T15 and J558. Early administration of this antibody also led to an enhancement of anti‐PC and anti‐Dex responses, apparently via expansion of a set of intermediate anti‐Id BD2‐like B cells. In adult mice it suppressed responses to both antigens. A third hybridoma FC4 (μ,χ), derived from 3‐day‐old spleen, reacts with GB4–10 as well as EB3–7 (anti‐J558). Introduction of this antibody into neonatal mice enhanced anti‐ Dex responses while in adults it caused suppression of T15 Id. The results presented here suggest a possible role for neonatal anti‐Id B cells in the primary activation of antigen‐reactive B cells by Id selection. Copyright © 1986 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
