IL-16 is constitutively present in peripheral blood monocytes and spontaneously released during apoptosis.

Constitutive expression of the pro-molecule of IL-16 has been found in T cells, mast cells, eosinophils, epithelial cells, fibroblasts, and dendritic cells. Here we show that IL-16 is also constitutively present in >98% of freshly isolated human CD14-positive peripheral blood monocytes when analyzed by flow cytometry. Because pro-IL-16 is cleaved to its bioactive mature form by caspase-3, and caspase-3 is also the pivotal effector of apoptosis in monocytes, we asked whether IL-16 release occurs in monocytes that undergo spontaneous apoptosis. As expected, freshly isolated, unstimulated monocytes underwent spontaneous caspase-3 activation. This apoptosis was paralleled by the loss of intracellular IL-16, as detected by flow cytometry, and the concurrent release of IL-16, as detected by ELISA. In contrast, stimulation with bacterial LPS inhibited caspase-3 activation and significantly inhibited the release of IL-16. As a specificity control, IL-1beta and IL-8 were not released during spontaneous monocyte apoptosis. In summary, our data demonstrate that monocytes contain IL-16 that is released during spontaneous apoptosis.

A novel P2X7 receptor activator, the human cathelicidin-derived peptide LL37, induces IL-1 beta processing and release.

The release of IL-1 beta is a tightly controlled process that requires induced synthesis of the precursor pro-IL-1 beta and a second stimulus that initiates cleavage and secretion of mature IL-1 beta. Although ATP as a second stimulus potently promotes IL-1 beta maturation and release via P2X(7) receptor activation, millimolar ATP concentrations are needed. The human cathelicidin-derived peptide LL37 is a potent antimicrobial peptide produced predominantly by neutrophils and epithelial cells. In this study, we report that LL37 stimulation of LPS-primed monocytes leads to maturation and release of IL-1 beta via the P2X(7) receptor. LL37 induces a transient release of ATP, membrane permeability, caspase-1 activation, and IL-1 beta release without cell cytotoxicity. IL-1 beta release and cell permeability are suppressed by pretreatment with the P2X(7) inhibitors oxidized ATP, KN04, and KN62. In the presence of apyrase, which hydrolyzes ATP to AMP, the effect of LL37 was not altered, indicating that LL37 rather than autocrine ATP is responsible for the activation of the P2X(7) receptor. We conclude that endogenous LL37 may promote IL-1 beta processing and release via direct activation of P2X(7) receptors.

HIV-1 infection does not impair human alveolar macrophage phagocytic function unless combined with cigarette smoking.

OBJECTIVE: Macrophages are an important reservoir for the HIV and contribute to innate lung defense by their ability to phagocytose, digest, and process invading pathogens. We hypothesized that HIV-1 infection may lead to a defect in the phagocytic activity of alveolar macrophages. DESIGN: In order to test this hypothesis, the phagocytic activity of alveolar macrophages from asymptomatic HIV-1 seropositive subjects was compared to healthy seronegative control subjects. Macrophages from one cohort were fed with Escherichia coli and from another cohort with opsonized sheep RBCs (SRBCs), and the phagocytic index was determined at different time intervals. SETTING: A tertiary-care, urban, university-based referral center. PARTICIPANTS: Asymptomatic HIV-1 seropositive subjects and healthy seropositive control subjects recruited from local community. RESULTS: No differences were found in the phagocytic activity between alveolar macrophages from the first cohort of eight seropositive and nine seronegative subjects. Although not statistically significant, there was a trend toward a lower phagocytic activity of HIV-positive smokers compared to HIV-positive nonsmokers. Opsonized phagocytic capacity (using opsonized SRBCs) was further analyzed in a second set of five HIV-positive subjects and five healthy control subjects. Whereas HIV status did not affect opsonized SRBC uptake, a history of smoking was associated with a statistically significant depression in phagocytic index. CONCLUSIONS: Although there is no significant impairment of phagocytic capacity in HIV-positive subjects compared to HIV-negative control subjects, cigarette smoking produces a significant depression in phagocytic activity that is amplified in HIV-positive smokers.