Cholecystokinin-Octapeptide (CCK-OP) and Substance P (SP) Influence Immune Response to Cholera Toxin in Live Animals

The immune response in the intestine is initiated by antigen uptake at the level of Peyer’s patches (PP)1 and along the small intestine.2,3 A series of initiating and enhancing signals are required to effect T cell activation by polypeptide antigens. A degree of antigen processing by the antigen-presenting cell (APC) to reveal epitopes reactive with the T cell receptor is usually required.4 Interaction of the processed antigen with the T cell receptor is regulated by products of the major histocompatibility complex residing in the APC surface membrane.5 Release by the APC of the cytokine IL-1 is required to induce the synthesis of receptors for IL-2 on the T cell.6 These processes regulate the subsequent production of specific antibodies by B cells. It may be desirable, in certain circumstances, to enhance the immune response. An obvious example is the administration of oral vaccines. On the other hand, there may be occasions when it is desired to abrogate the immune response, for instance, in order to prevent hypersensitivity responses. One method of enhancing the immune response in the intestine is by the concomitant administration of the antigen with an appropriate adjuvant. In this report, we wish to investigate the potential adjuvant effect of some peptide hormones in regulating the immune response to foreign antigens in the intestine. We chose the peptide hormones, substance P (SP) and cholecystokinin- octapeptide (CCK-OP) as well as their respective antagonists, spantide and L 316,718. In addition, we investigated the effect of capsaicin, which is a toxin to SP containing-nerve fibers.