Tuberculous pleuritis is a good model for the study of specific cells at the site of active Mycobacterium tuberculosis (Mtb) infection. We investigated the frequency and phenotype of NK cells in paired samples of peripheral blood and pleural fluid (PF) from patients with tuberculosis (TB) or parapneumonic infection. We demonstrated for the first time a reduction of NK cells in PF from TB with an enrichment in the CD56brightCD16− subset. In agreement, in PF NK cells we observed an increased expression of CD94, NKG2A, CD62L, and CCR7 molecules and lower expression of Bcl-2 and perforin. The activation markers CD69 and HLA-DR were also increased. The enrichment in the CD56bright subset was due to an increased susceptibility to apoptosis of CD56+CD16+ NK cells mediated by heat-labile and stable soluble factors present in tuberculous effusions and not in PF from other etiologies. Furthermore, in TB patients, Mtb-induced IFN-γ production by PF NK cells was not dependent on the presence of CD3+, CD19+, and CD14+ cells, suggesting a direct interaction of CD56bright cells with Mtb and/or the involvement of other accessory cells present at the site of Mtb infection.

Photodynamic antimicrobial chemotherapy (PACT) is a potential antimicrobial therapy that combines light and a photosensitizing drug, promoting a phototoxic effect on the treated cells, in general via oxidative damage. In this work we studied the effect of PACT, using methylene blue (MB), on the permeability of Candida albicans membrane. Our results demonstrated that the combination of MB and laser (684 nm) promoted a decrease in Candida growth. The inhibition was more pronounced in the presence of 0.05 mg/ml MB and with an energy density of 28 J/cm(2). The decrease in Candida growth was associated with an increase in membrane permeabilization. Thus, we suggest that a PACT mechanism using MB can be related to damage in the plasma membranes of the cells.

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Tuberculous pleuritis usually shows lymphocytic preponderance, but neutrophils are also present. Therefore, pleuritis is a good model for the study of neutrophil fate at sites of active Mycobacterium tuberculosis infection. We have previously demonstrated in vitro that M. tuberculosis-induced neutrophil apoptosis involves p38 mitogen protein kinase activation through Toll-like receptor 2. Herein, we demonstrate that, in tuberculous pleuritis, neutrophil apoptosis increases together with the expression of Toll-like receptor 2 and phosphorylated p38 (p-p38) kinase. In addition, receptors associated with activation/apoptotis (CD11b, CD64, tumor necrosis factor receptor, and Fas ligand) are up-regulated, together with a loss of CD16 expression. However, neutrophils express CD86, CD83, and major histocompatibility complex class II antigens, acquiring dendritic cell (DC) characteristics. Therefore, the cytokine milieu in the pleural space may influence signaling pathways on activated neutrophils, thereby inducing apoptosis and inhibiting their proinflammatory capacity, as well as allowing them acquire DC characteristics that influence the immune response.