Adrenocorticotropin (ACTH) functions as a late-acting B cell growth factor and synergizes with interleukin 5

In recent years there has been considerable discussion of possible cross-regulatory mechanisms involving the immune system and the neuroendocrine system. Certainly, evidence of hormonal communication between these two systems would provide at least a partial explanation for the many anecdotal observations of physical and mental stress affecting disease course. In previous studies of a neoplastic lymphokine-responsive B cell clone, BCL1-3B3, we noted that these cells produced a lymphokine which could affect normal B cell growth and viability. Physical characterization of this lymphokine indicated that its molecular weight was identical to that of the neuroendocrine hormone adrenocorticotropin (ACTH). Since Blalock and colleagues had reported the production of ACTH by virally-infected B cells, we have investigated whether ACTH can functionally mimic the BCL1-3B3-derived lymphokine. The neuroendocrine hormone adrenocorticotropin (ACTH) can increase in vitro murine B lymphocyte proliferation when added at physiologically relevant concentrations between 10(-9) to 10(-11) M. ACTH does not mimic the action of any lymphokine known to be required for B cell proliferation such as IL-2, IL-4, or IL-5. ACTH requires the presence of one or more of these known B cell stimulatory factors for its action and the most marked increase in B cell proliferation were noted in assays for IL-5 activity where 10(-10) M ACTH increased thymidine incorporation up to five-fold. Using two-stage assays, we determined that ACTH acts during the latter stages of B cell activation (i.e., 3-4 days after initial stimulation with either the combination of IL-4, GAMIg-Sepharose, and IL-1 or the combination of DxS and IL-5). These data indicate a direct role for a stress-induced neuroendocrine hormone in modulating the course of a humoral immune response.