Figure 1311

Macrophage activation by a helper CD4; T cell. Helper CD4+ T lymphocytes recognize the bacterial antigen expressed in the context of MHC II molecules on the surface of a macrophage that has phago-cytosed the bacteria. The recognition of MHC II molecules activates the T cell, which in turn secretes IL-2. IL-2 acts as an autocrine hor mone to stimulate T cell division and differentiation. Newly formed helper CD4+ T lymphocytes also interact with MHC II molecules and release interferon y (IFN-y). This cytokine stimulates the macrophage to destroy the bacteria inside its phagosomes. CD4 molecules on the surface of the T cell also potentiate antibacterial reactions.

Lymphocytes circulate through both lymphatic and blood vessels

The circulation of lymphocytes through the lymphatic vessels and the bloodstream enables them to move from one part of the lymphatic system to another at different stages in their development and to reach sites within the body where they are needed. Lymphocytes conveyed in the lymph enter lymph nodes via afferent lymphatic vessels, while lymphocytes conveyed in the blood enter the node high endothelial venule afferent lymphatic vessels right lymphatic trunk high endothelial venule afferent lymphatic vessels right lymphatic trunk

.heart aorta

.heart aorta

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