Abstract
The in vitro stimulation of isolated B cells in fragment cultures has permitted the analysis of splenic B cells obtained from neonates and immune or non-immune adults with respect to several characteristics including a) specificity and hapten inhibitability of stimulation, b) dependence of stimulation on antigen concentration and carrier recognition, c) burst size and longevity of clones derived from stimulated cells, and d) immunoglobulin class and affinity of the antibody produced by such clones. The results indicate that there exist at least three types of B cells one of which predominates in spleens of neonates (neonatal B cells), a second which predominates in spleens of non-immune adults (primary B cells) and a third predominating in spleens of immune mice (secondary B cells).