[The body's defense against intracellular bacteria].

The separation of the two pathways of differentiation of CD4 T cells is fundamental to an understanding of host defence against intracellular bacteria. Th1 cells, but not Th2 cells, promote effective host response. Elucidation of the mechanisms responsible for the differentiation of Th1 and Th2 cells will facilitate the development of subcellular vaccines against intracellular bacteria.