The roles of T cell factors in activation, cell cycle progression, and differentiation of human B cells

The relationship of the T cell influences involved in human B cell activation and differentiation into immunoglobulin-secreting cells (ISC) was investigated. T cell supernatants (T supt) generated by stimulating T cells with phytohemagglutinin and phorbol myristate acetate contained activities capable of augmenting DNA synthesis and the growth of mitogen-stimulated B cells and supporting the differentiation of ISC. To examine the role of T supt in B cell activation and the progression through the cell cycle, T cell- and monocyte-depleted B cells were stimulated with formalinized Cowan I strain Staphylococcus aureus (SA), and the percentages of cells in G1, S, and G2 + M were determined by acridine orange staining and analysis. In all experiments, a similar percentage of cells entered G1 during the first 24 to 36 hr of culture when stimulated with SA or SA + T supt. Similar results were seen when B cell activation was analyzed by acquisition of a number of other markers of cell activation. Analysis of cell cycle progression with mithramycin staining of cellular DNA in the presence or absence of vinblastine to arrest mitosis indicated that SA-activated B cells were able to complete S and divide in the absence of T supt. Although an effect of T supt on the progression of B cells through the S phase was evident during the first cell cycle, the major effect only became apparent after the first round of cell division. Although T supt was not necessary for initial B cell activation, T cell influences were absolutely necessary for the differentiation of ISC. T supt did not need to be present during the initial 24 to 36 hr of incubation to permit subsequent generation of ISC. However, when T supt was present initially, an increased number of ISC were produced. Hydroxyurea elimination of cells traversing the G1-S interphase indicated that reception of the differentiation signal occurred before the S phase, but that the generation of ISC required subsequent DNA synthesis and/or cell division. Although precursors of ISC were entirely contained within the population triggered to divide by SA alone, there was no preferential expansion of such precursors as a result of SA stimulation. These results indicate that T cell signals are not absolutely necessary for initial B cell activation and progression through the first cell cycle, although T cell factors promote DNA synthesis by some activated B cells. In contrast, differentiation into ISC is completely dependent on T cell influences.(ABSTRACT TRUNCATED AT 400 WORDS)