Interplay of Trypanosome Lytic Factor and innate immune cells in the resolution of cutaneous Leishmania infection.

Trypanosome Lytic Factor (TLF) is a primate-specific high-density lipoprotein (HDL) complex that, through the cation channel-forming protein apolipoprotein L-1 (APOL1), provides innate immunity to select kinetoplastid parasites. The immunoprotective effects of TLF have been extensively investigated in the context of its interaction with the extracellular protozoan Trypanosoma brucei brucei, to which it confers sterile immunity. We previously showed that TLF could act against an intracellular pathogen Leishmania, and here we dissected the role of TLF and its synergy with host-immune cells. Leishmania major is transmitted by Phlebotomine sand flies, which deposit the parasite intradermally into mammalian hosts, where neutrophils are the predominant phagocytes recruited to the site of infection. Once in the host, the parasites are phagocytosed and shed their surface glycoconjugates during differentiation to the mammalian-resident amastigote stage. Our data show that mice producing TLF have reduced parasite burdens when infected intradermally with metacyclic promastigotes of L. major, the infective, fly-transmitted stage. This TLF-mediated reduction in parasite burden was lost in neutrophil-depleted mice, suggesting that early recruitment of neutrophils is required for TLF-mediated killing of L. major. In vitro we find that only metacyclic promastigotes co-incubated with TLF in an acidic milieu were lysed. However, amastigotes were not killed by TLF at any pH. These findings correlated with binding experiments, revealing that labeled TLF binds specifically to the surface of metacyclic promastigotes, but not to amastigotes. Metacyclic promastigotes of L. major deficient in the synthesis of surface glycoconjugates LPG and/or PPG (lpg1- and lpg5A-/lpg5B- respectively) whose absence mimics the amastigote surface, were resistant to TLF-mediated lysis. We propose that TLF binds to the outer surface glycoconjugates of metacyclic promastigotes, whereupon it kills the parasite in the acidic phagosome of phagocytes. We hypothesize that resistance to TLF requires shedding of the surface glycoconjugates, which occurs several hours after phagocytosis by immune cells, creating a relatively short-lived but effective window for TLF to act against Leishmania.

Apolipoproteins L1-6 share key cation channel-regulating residues but have different membrane insertion and ion conductance properties.

The human apolipoprotein L gene family encodes the apolipoprotein L1-6 (APOL1-6) proteins, which are effectors of the innate immune response to viruses, bacteria and protozoan parasites. Due to a high degree of similarity between APOL proteins, it is often assumed that they have similar functions to APOL1, which forms cation channels in planar lipid bilayers and membranes resulting in cytolytic activity. However, the channel properties of the remaining APOL proteins have not been reported. Here, we used transient overexpression and a planar lipid bilayer system to study the function of APOL proteins. By measuring lactate dehydrogenase release, we found that APOL1, APOL3, and APOL6 were cytolytic, whereas APOL2, APOL4, and APOL5 were not. Cells expressing APOL1 or APOL3, but not APOL6, developed a distinctive swollen morphology. In planar lipid bilayers, recombinant APOL1 and APOL2 required an acidic environment for the insertion of each protein into the membrane bilayer to form an ion conductance channel. In contrast, recombinant APOL3, APOL4, and APOL5 readily inserted into bilayers to form ion conductance at neutral pH, but required a positive voltage on the side of insertion. Despite these differences in membrane insertion properties, the ion conductances formed by APOL1-4 were similarly pH-dependent and cation-selective, consistent with conservation of the pore-lining region in each protein. Thus, despite structural conservation, the APOL proteins are functionally different. We propose that these proteins interact with different membranes and under different voltage and pH conditions within a cell to effect innate immunity to different microbial pathogens.

Microbial study of hospital environment and carrier pattern study among staff in Nepal Medical College Teaching Hospital.

The present study was done to see the microbial flora in the environment (air and surface) of Nepal Medical College Teaching Hospital and the staffs working in the hospital. Altogether 160 environmental (air n = 43, surface n = 117) samples were collected and studied from different wards. Similarly 150 samples (48 nasal swabs, 48 throat swabs and 54 hand samples) from the staffs were collected and studied following the standard microbiological protocols. Gram +ve cocci were the most predominant ones among the bacterial isolates from the environment followed by gram +ve bacilli and gram -ve bacilli. Among fungal isolates, yeast were the most common isolates while Aspergillus spp. were the most frequently occurring mold. Out of 150 samples collected for the study of carrier pattern, 32 out of 54 samples collected were found to have Staphylococcus aureus in their hands, 1 had Escherichia coli. Other isolates were Bacillus spp., Micrococci and coagulase negative staphylococci. Similarly 21 (43.8%) out of 48 nasal samples were found to have S. aureus while none of the staffs were found to have beta-hemolytic streptococci in their throat. In the study, 1.6% environmental isolates and 5.7% carrier isolates of S. aureus were found to be Methicillin resistant.