BOVINE TYPE-I AND TYPE-2 RESPONSES

The Th1/Th2 paradigm has provided a useful framework for understanding the observed bias in immune responses that are often dominated by eit her cell-mediated or humoral responses, and for devising therapeutic s trategies to stimulate T cell- or antibody-mediated immunity. However this paradigm is an oversimplification of a much more complex immunore gulatory network. Studies with bovine Tn cell clones and immunoregulat ory cytokines support this viewpoint. This paper highlights the progre ss that has been made in defining type 1 and type 2, responses in catt le. Evidence is presented for the presence of different subtypes of an tigen-specific Th cell clones of cattle which constitute a spectrum of cell phenotypes, and for cytokine-mediated regulation of Th cell resp onses that differs from that observed in mice. The majority of over 60 parasite antigen-specific Th cell clones coexpress IL-4 and IFN-gamma , and polarized cytokine profiles were rarely observed. Furthermore, I L-2 and IL-10 expression was not restricted to IFN-gamma or IL-4-produ cing cells, respectively. This lack of coordinate regulation of ''Th1' ' and ''Th2'' cytokines strengthens the emerging viewpoint that Th1 an d Th2 responses, per se, do not typify the immune response to most pat hogens. In addition, we provide evidence that major regulatory cytokin es, IL-4, IL-10, and IL-12, do not selectively exert their negative (I L-4 and IL-10) or positive (IL-12) effects on Th1-like cells. (C) 1998 Elsevier Science B.V. All rights reserved.