Figure 2.

Naive CD4⁺CD8⁻ thymocytes are less potent in providing in vivo B cell help than primed peripheral CD4⁺ T cells. Primed CD4⁺ T cells and primed B cells were negatively selected from TDLs from PVG.RT1^c rats primed with 10⁸ SRBC 4–9 wk before cannulation. Naive CD4⁺CD8⁻ thymocytes were negatively selected from thymus of normal PVG.RT1^c rats by rosette depletion as described in Materials and Methods. Syngeneic recipients were given 800 rads and injected i.v. 1 d later with 10⁸ SRBC, 3 × 10⁷ SRBC-primed B cells and either three different doses of SRBC-primed CD4⁺ peripheral T cells or three different doses of naive CD4⁺CD8⁻ thymocytes. The controls were given 10⁸ SRBC and 3 × 10⁷ SRBC-primed B cells. The recipients were bled 7 d later and the anti-SRBC antibody titers determined by radioimmunoassay. The results are expressed in arbitrary units made by comparison with a pool of sera from rats immunized with SRBC.