A major function of Th1 cells is to both promote phagocytosis of microbes and the killing of intracellular microbes.
1. Bacteria are engulfed by a macrophage
and placed in a phagosome. A lysosome fuses with the phagosome forming a phagolysosome.
2.An activated Th1
lymphocyte binds to a peptide/MHC-II complex on a macrophage by way of its TCR
and CD4 molecule.
3.Co-stimulatory
molecules such as CD40L on the Th1 cell then bind to CD40
on a macrophage.
4. The Th1 lymphocyte secretes the cytokine interferon-gamma (IFN-gamma)
that binds to IFN-gamma receptors receptors on the macrophage.
5. The IFN-gamma activates the macrophage enabling it to produce more hydrolytic
lysosomal enzymes, nitric oxide, and toxic oxygen radicals that destroy the
microorganisms within the phagosomes and phagolysosomes.