In vivo generated Th1 cells can migrate to B cell follicles to support B cell responses.

The description of Th1 and Th2 T cell subsets rationalized the inverse correlation between humoral and cell-mediated immunity. Although Th1 cells were described to support cell-mediated immune responses, their role in supporting certain B cell responses was firmly established. However, there is now a prevailing preconception that provision of B cell help is entirely the domain of Th2 cells and that Th1 cells lack this capacity. Previous studies demonstrated that immunization using aluminum hydroxide adjuvants induces Ag-specific Th2 responses, whereas incorporation of IL-12 with aluminum hydroxide produces a Th1 inducing adjuvant. By immunizing TCR transgenic recipient mice in this fashion, we have generated Ag-specific, traceable Th1 and Th2 cells in vivo and assessed their follicular migration and ability to support B cell responses. In this study we have shown that in vivo polarized Th1 and Th2 cells clonally expand to similar levels and migrate into B cell follicles in which they support B cell responses to a similar degree. Critically, we present direct evidence that in vivo polarized, IFN-gamma secreting Th1 cells migrate into B cell follicles where they can interact with Ag-specific B cells.