Date of Award:

5-1-1993

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology (Molecular Biology)

Committee Chair(s)

Vijendra K. Singh

Committee

Vijendra K. Singh

Committee

Gregory J. Podgorski

Committee

Reed P. Warren

Committee

Raghubir P. Sharma

Committee

Dennis J. Odell

Abstract

Relationships between neuroendocrine and immune systems prompted this study of the immunomodulatory role of corticotropin-releasing factor (CRF), a peptide hormone of the neuroendocrine system. This research investigated the effect of CRF on the in vitro synthesis of interleukins (interleukin-1[IL-1], interleukin-2 [IL-2] and interleukin-6 [IL-6)), natural killer (NK) cell activity, antibody production, and cAMP accumulation in immunocytes. CRF (l0-9 M) induced bioactive cytokines like IL-1, IL-2, and IL-6 in peripheral blood mononuclear cells (MNC) from healthy subjects. Two structurally related peptides (TyrCRF and α-helical-CRF9-41) also elicited 16- to 21-fold stimulation of IL-6. CRF stimulated purified monocytes, but not lymphocytes, for IL-6 production. CRF in nanomolar concentrations caused a significant (p ≤ 0.05) increase in the cell mediated lysis (CML) of NK cells, but required a preincubation of about 18 hours. This stimulatory effect was inhibited by monocyte-depletion or antibodies to IL-1 or antibodies to β-endorphin, and it was reconstituted by monocyte-derived IL-1. An interpretation of these results is that IL-1 and β-endorphin act as the mediators of NK cell stimulation by CRF. Regarding the synthesis of antibodies (IgM, IgG, and IgA), CRF exhibited an immunosuppressive effect. At concentrations of I0-13 M or greater, CRF and three structurally related peptides (Tyr-CRF, α-helical CRF9-41, and sauvagine) significantly (p ≤ 0.001) suppressed the synthesis of antibodies. The antibody synthesis was also inhibited by monocyte-depletion or antibody to IL-1 or antibody to β-endorphin, but neither treatment counteracted the suppressive effect of CRF. The IgG synthesis inhibition by CRF was not counteracted by antagonist a-helical CRF9-41, indicating the involvement of a different CRF receptor subtype than the conventional type of CRF receptors. The CRF treatment of cells significantly (p=0.019) stimulated the intracellular levels of cAMP. This effect occurred almost exclusively in purified monocytes, but not in lymphocytes. The CRF-induced increase of cAMP was antagonized by a-helical CRF9-41. The stimulated level of cAMP was furthermore augmented by pretreatment of MNC with a cAMP-dependent protein kinase (PKA) peptide inhibitor (PI20), but was virtually unaffected by protein kinase C (PKC) inhibitor H7, and was reduced to baseline by an intracellular Ca++ antagonist HA1004. These findings provide evidence that cAMP alone or by interaction with Ca++ plays a second messenger role in the CRF-signaling pathway. Finally, it is concluded that CRF modulates immune functions through a biphasic response, i.e. an irnmunosuppressive effect (inhibition of antibody synthesis) in lower concentrations and an immunostimulatory effect (induction of cytokine synthesis and increase of NK cell activity) in higher concentrations. Hence, CRF through monocyte activation of IL-1 and IL-6 synthesis may function as a soluble messenger in the neuroendocrine-immune circuitry.

Download

Share

COinS

Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .