Changes with in vitro Activation of the B Cell Panel Antigens

Abstract

With exposure to specific antigenic or mitogenic stimuli, B cells proliferate and subsequently differentiate into antibody-secreting cells. The initial events which accompany activation include an increase in cell size, augmented DNA and RNA synthesis, and changes in cell surface structures. The expression of surface immunoglobulin (SIg) and la, the classical surface markers of B cells, has been extensively studied during in vitro stimulation. Upon activation, resting B cells which express IgM and/or IgD will lose SIgD, and then no longer express membrane Ig or switch to the expression of other isotypes (1). Similarly, resting B cells continue to express la after activation until the plasma cell stage (2). In our laboratory, utilizing a panel of monoclonal antibodies directed against B cell differentiation antigens, we have noted changes in the cell surface pheno- type of resting B cells with activation. Two B cell-restricted antigens, B1 and B4, have been observed to be expressed on resting and activated B cells, and lost prior to the terminal stages of differentiation (3,4). The B2 antigen, present on resting cells is lost during the early stages of activation (4,5). We and others have described additional antigens which are not expressed on resting B cells but only appear with activation. These acti-vation antigens include B-LAST 1 (6), B5 (7), interleukin-2 receptor (IL- 2R) (8,9), BB1 (10), 4F2 (11), and the transferrin receptor (11).