CD4 and infection: The beneficial, seemingly paradoxical, effects of hypoxia to the host are that hypoxia can: (i) impair the growth of Mtb as evinced by Mtb-infected mice, guinea pigs, & rabbits controlled the TB significantly better when breathing 10% O2 (vs. 21% O2) (265); (ii) induce expression of HIF-1α, augmenting phagocytes to kill Mtb in part through impaired ability to activate autophagy (158, 162) (see also HIF-1α below); (iii) recruit immune cells to infection site through induction of the chemokine receptor CXCR4 for CD4+ T cells (164) & neovascularization (165).