SYNERGISTIC EFFECT OF POKEWEED MITOGEN AND S. AUREUS COWAN I IN VITRO BLOOD B CELL DIFFERENTIATION

Abstract

Neonatal B cells, unlike adult B cells, do not develop into immunoglobulin secreting plaque forming cells when cultured in the presence of pokeweed mitogen alone or killed S. aureus Cowan I alone. We found that simultaneous addition of these two B cell activators significantly increased the development of plaque forming cells in cord blood mononuclear cells. In 55 neonate cultures, pokeweed mitogen and S. aureus Cowan I together induced 7114(±10,077) plaque forming cells/10⁶ cord blood mononuclear cells, compared to 875(±2527) with pokeweed mitogen alone or 672(±1590) with S. aureus Cowan I alone. This effect was not seen with adult cells. Additional experiments indicate that the synergistic effect of pokeweed mitogen and S. aureus Cowan I on cord blood mononuclear cells can best be explained by a two-phase model of B cell differentiation wherein the macrophage and its soluble product governs an early first phase, while the T helper and its soluble mediator governs the later second stage. We propose that in the neonate, S. aureus Cowan I acts on the macrophage to initiate the differentiation, and pokeweed mitogen acts on the T helper to complete the development into plaque forming cells.

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