One bacterial pneumonia event among 365 patients was reported from Thailand which recruited the majority of patients of Asian ethnicity. Rates of PcP prophylaxis were lower in Thailand (0.8%) compared with other countries (6.7%) in which study participants

were enrolled, and this lower use of PcP prophylaxis, if anything, could potentially favour an increased risk of bacterial pneumonia; geographical and other country characteristics are potential confounders. In ESPRIT, more recent receipt of rIL-2 was associated with Selleck Ceritinib a greater risk of bacterial pneumonia, although the confidence intervals were very wide. The reasons why more recent receipt of rIL-2 is associated with increased risk of pneumonia are uncertain, but there are a number of potential STA-9090 solubility dmso mechanisms. Polymorphonuclear neutrophils (PMNs) are a major effector cell against pathogenic bacteria, including those causing pneumonia; the T-cell response [17] is also thought to be important in the normal immune response to pneumococci. IL-2 may activate PMNs by inducing the secretion of tumour necrosis factor alpha [15], thus contributing to protective immunity, but at higher doses (600 000 IU/kg) IL-2 causes a chemotaxis defect which impairs neutrophil function. Recent data in mice show that exogenous

IL-2 can impair sequestration of neutrophils into the peritoneal cavity, although the same effect Tyrosine-protein kinase BLK was not seen in the lung in response to lipopolysaccharide-induced inflammation [18]. In ESPRIT, as in the SMART study, detectable HIV viraemia was associated with an increased risk of bacterial pneumonia event. Gordin et al. [12] suggested that increased inflammatory markers (IL-6 and D-dimer) in patients with detectable HIV replication might be associated with higher rates of bacterial pneumonia, although there was no direct evidence in support of this. Porter et al. [19] have recently demonstrated that, in a group

of patients exposed to rIL-2 with cART, there were significant increases in high-sensitivity C Reactive Protein and D-dimer occurring by the end of the initial rIL-2 cycle and these increases were independent of changes in VL, CD4 cell count and T-cell proliferation. These findings suggest the following might in part explain the increased hazard of bacterial pneumonia associated with very recent receipt of rIL-2. First, the inflammatory surge associated with recent interleukin-2 receipt [19–24], second, the transient burst of HIV-viraemia known to occur around rIL-2 dosing cycles [20] and last, impairment of neutrophil function associated with rIL-2 exposure. Overall, however, it is harder to explain why the increased risk associated with rIL-2 receipt should continue for several months after the dosing cycle and long after the die-back of secondary cytokines and the reduction in immune activation that occur following rIL-2 exposure [20,25].