Induction of antigen-specific antibody responses in primed and unprimed B cells. Functional heterogeneity among Th1 and Th2 T cell clones.

CD4+ T cells have been recently divided into two subsets. The functions of these subsets are thought to be distinct: one subset (Th1) is responsible for delayed type hypersensitivity responses and another (Th2) is primarily responsible for induction of antibody synthesis. To more precisely define the roles of both subsets in humoral immune responses, we examined the ability of a panel of nominal antigen specific Th1 and Th2 clones to induce anti-TNP specific antibody synthesis in TNP-primed or unprimed B cells. Four of nine Th1 clones induced little or no antibody synthesis with TNP-primed B cells. However, five other Th1 clones were very effective at inducing IgG anti-TNP plaque-forming cell (PFC) responses in primed B cells. One of these Th1 clones was analysed in detail and found to also provide helper function for unprimed B cells. Cognate B-T cell interaction was required for induction of both primary and secondary responses with this clone, indicating that a Th1 clone could function as a "classical" Th cell. The seven IL-4 producing Th2 clones examined were also heterogeneous in their ability to induce antibody secretion by TNP-primed B cells. Although four of the Th2 clones induced IgG and IgM anti-TNP PFC responses, two Th2 clones induced only IgM and no IgG antibody, and another clone failed to induce any anti-TNP PFC. All Th2 clones failed to induce any anti-TNP PFC. All Th2 clones produced high levels of IL-4, but "helper" Th2 clones produced significantly greater amounts of IL-5 than "non-helper" Th2 clones. These studies indicate that some IL-2- and some IL-4-producing T cell clones can induce TNP-specific antibody in cell clones can induce TNP-specific antibody in primed and unprimed B cells, and that Th1 and Th2 clones are heterogeneous in their ability to induce Ig synthesis. Therefore, although T cell clones can be classified as Th1 or Th2 types according to patterns of IL-2, IFN-gamma, or IL-4 synthesis, the functional capacity to induce antibody synthesis cannot be predicted solely by their ability to secrete these lymphokines.