The innate immune response in human tuberculosis is not completely understood. To improve our knowledge regarding the role of cathelicidin hCAP-18/LL37 in the innate immune response to tuberculosis infection, we used immunohistochemistry, immunoelectron microscopy, and gene expression to study the induction and production of the antimicrobial peptide in A549 epithelial cells, alveolar macrophages (AM), neutrophils, and monocyte-derived macrophages (MDM) after infection with Mycobacterium tuberculosis. We demonstrated that mycobacterial infection induced the expression and production of LL-37 in all cells studied, with AM being the most efficient. We did not detect peptide expression in tuberculous granulomas, suggesting that LL-37 participates only during early infection. Through the study of Toll-like receptors (TLR) in MDM, we showed that LL-37 can be induced by stimulation through TLR-2, TLR-4, and TLR-9. This last TLR was strongly stimulated by M. tuberculosis DNA. We concluded that LL-37 may have an important role in the innate immune response against M. tuberculosis.

The capacity of Mycobacterium tuberculosis (MTB) to induce production of chemokines with known chemotactic activity for monocytes and lymphocytes, the cellular building blocks of granulomas, was investigated. These chemokines included regulated upon activation, normal T cell expressed and secreted (RANTES), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1alpha (MIP-1alpha). MTB stimulated production of MCP-1 and MIP-1alpha by blood monocytes (MN) and alveolar macrophages (AM). MTB infection of MN and AM stimulated release but not production of RANTES. AM produced or released significantly higher levels than MN of RANTES (by 2.1-fold), MCP-1 (by 6.9-fold), and MIP-1alpha (by 5. 5-fold) (P < 0.05 for each). This study also confirmed that MTB-infected AM produce the chemokine interleukin (IL)-8. MTB infection of AM resulted in increased steady-state expression of messenger RNA (mRNA) for MCP-1 and MIP-1alpha and minimal increased expression of RANTES mRNA. Both an avirulent (H37Ra) and a virulent (H37Rv) strain of MTB and purified protein derivative of H37Rv but not latex beads induced production of chemokines. Supernatants of MTB-infected cells demonstrated chemotactic activity for both monocytes and lymphocytes partially inhibitable by neutralizing antibodies against the chemokines studied. Bronchoalveolar lavage fluid from patients with active pulmonary tuberculosis as compared with healthy control subjects contained increased levels of RANTES (by 8-fold), MCP-1 (by 2.7-fold), and IL-8 (by 8.9-fold) (P < 0.05), but not MIP-1alpha, as compared with healthy control subjects. Thus, multiple chemokines may be involved in recruitment of cells for granuloma formation in tuberculosis.

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BackgroundCD33 is a membrane receptor containing a lectin domain and a cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) that is able to inhibit cytokine production. CD33 is expressed by monocytes, and reduced expression of CD33 correlates with augmented production of inflammatory cytokines, such as IL-1β, TNF-α, and IL-8. However, the role of CD33 in the inflammation associated with hyperglycemia and diabetes is unknown. Therefore, we studied CD33 expression and inflammatory cytokine secretion in freshly isolated monocytes from patients with type 2 diabetes. To evaluate the effects of hyperglycemia, monocytes from healthy donors were cultured with different glucose concentrations (15-50 mmol/l D-glucose), and CD33 expression and inflammatory cytokine production were assessed. The expression of suppressor of cytokine signaling protein-3 (SOCS-3) and the generation of reactive oxygen species (ROS) were also evaluated to address the cellular mechanisms involved in the down-regulation of CD33.ResultsCD33 expression was significantly decreased in monocytes from patients with type 2 diabetes, and higher levels of TNF-α, IL-8 and IL-12p70 were detected in the plasma of patients compared to healthy donors. Under high glucose conditions, CD33 protein and mRNA expression was significantly decreased, whereas spontaneous TNF-α secretion and SOCS-3 mRNA expression were increased in monocytes from healthy donors. Furthermore, the down-regulation of CD33 and increase in TNF-α production were prevented when monocytes were treated with the antioxidant α-tocopherol and cultured under high glucose conditions.ConclusionOur results suggest that hyperglycemia down-regulates CD33 expression and triggers the spontaneous secretion of TNF-α by peripheral monocytes. This phenomenon involves the generation of ROS and the up-regulation of SOCS-3. These observations support the importance of blood glucose control for maintaining innate immune function and suggest the participation of CD33 in the inflammatory profile associated with type 2 diabetes.

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