Elevated substance P levels in HIV-infected men.

The neuropeptide, substance P, is a potent modulator of neuroimmunoregulation. Substance P and its receptor modulate HIV infection. HIV-seropositive men had significantly higher plasma substance P levels compared with uninfected controls, which were associated with decreased CD16 and CD56 natural killer (NK) cell populations. The changes in plasma substance P levels and decreases in NK subsets did not correlate with CD4 cell levels, but a diurnal pattern was suggested for substance P. The balance between substance P expression and functions of immune cells may be important in the immunopathogenesis of HIV infection.