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-γ) that binds to IFN-γ receptors receptors on the macrophage.
5. The IFN-γ 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.