HIV Induces both a Down‐Regulation of IRAK‐4 that Impairs TLR Signalling and an Up‐regulation of the Antibiotic Peptide Dermcidin in Monocytic Cells

Abstract

HIV-infected individuals have an increased risk of invasive bacterial infections, even at early clinical stages with relatively normal CD4(+) T-cell counts. The pathogenic mechanisms behind this are not fully understood. However, an increasing number of studies indicate that HIV may impair the innate immunity to bacteria by infecting key cells of the monocyte/macrophage lineage. In this study, the effects of HIV infection on the protein profile of undifferentiated monocyte-like THP-1 cells were examined by a mass spectrometric approach based on stable isotope labelling with amino acid in cell culture (SILAC). We identified 651 proteins, of which nine proteins were down-regulated and 17 proteins were up-regulated in HIV-infected THP-1 cells as compared to uninfected controls. Most remarkably, the IL-1 receptor associated kinase 4 (IRAK-4), which is essential for virtually all TLR signalling, was suppressed, whereas the precursor for the antibiotic peptide Dermcidin was up-regulated in HIV-infected cells. Upon stimulation of either TLR2 or TLR4, the HIV-infected THP-1 cells displayed reduced TNF-alpha secretion. The HIV-induced down-regulation of IRAK-4 was reconfirmed in monocyte-derived macrophage cell cultures. These data suggests that HIV may impair the TLR signalling cascade for pathogen recognition in cells of the monocyte/macrophage lineage and thus, may reduce the ability of the innate immune system to sense invading pathogens and initiate appropriate responses.