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Activation of polymorphonuclear cells (PMNs) leads to the formation of superoxide, which is in turn dismutated to H2O2 by superoxide dismutase (SOD) and is partly responsible for oxygen-dependent microbicidal activity. However, no comparative information is available on the effect of SOD inhibition before PMN activation to allow simulation of the SOD defects that are known to occur in some ruminants. This paper attempts to examine the degranulative and phagocytic responses in buffalo, cattle and goat PMNs exposed to diethyldithiocarbamate, a known SOD inhibitor. The activity of glutathione peroxidase and reductase was increased in the presence of SOD inhibitor. On activation, H2O2 production increased significantly (p < 0.01), while SOD inhibition before the activation of PMNs caused a significant decline in the production of H2O2 (p < 0.05) in all the species studied. There was a significant increase (p < 0.05) in the phagocytosis of Candida albicans spores by buffalo PMNs activated with opsonized zymosan. Activation of bovine PMNs after exposure to the SOD inhibitor resulted in a significant decline (p < 0.05) in phagocytic activity; in the other species, the two values only approached significance. Among the activators, opsonized zymosan caused a significant increase in phagocytic activity as compared to lipopolysaccharide, particularly in the PMNs of buffaloes (p < 0.05). Increased fungicidal activity (p < 0.05) occurred with opsonized zymosan-activated PMNs of all the species studied. The fungicidal activity was found to decline in PMNs exposed to SOD inhibitor before activation (p < 0.05). Interestingly, the phagocytic activity of caprine PMNs was found to be lower than that of PMNs from cattle (p < 0.05).

β-Defensin antimicrobial peptides are multifunctional biomolecules, which are a major component of the oxygen-independent microbicidal system of buffalo polymorphonuclear (PMN) cells. They have great potential for use as proteomic biomarkers of host cell responses in the presence of microbial agents. On purifying these peptides by RP-HPLC, four defensin peptides were revealed. The results from testing against Escherichia coli, Staphylococcus aureus, Streptococcus pyogenes, Candida albicans, Rinderpest Virus (RPV) and Newcastle Disease Virus (NDV), showed that the peptides possessed antimicrobial and antiviral activities. Minimum inhibitory concentration (MIC) values varied according to the peptide amounts and the exposure time. Furthermore, an increase in the levels of these cationic antimicrobial peptides was apparent in milk obtained from natural cases of mastitis, as compared to the levels in normal milk. MALDI-TOF-based amino acid sequencing confirmed the expression of two β-defensins (LAP and BNBD-2) in mastitis milk. A comparison of peptide sequences revealed that buffalo LAP and BNBD-2 share 98.6% and 100% sequence identity, respectively, with those of cattle. In vitro, Bovine Viral Diarrhoea Virus (BVDV) infection was shown to induce the expression of the β-defensin gene, as evidenced by the PCR amplification of cDNA with specific primers. The determination of the enhanced expression of β-defensin peptides in mastitis milk and in PMN cells, can be considered as an advanced approach to the assessment of cellular and molecular responses to cell injury. It is hoped that in vitro studies on phagocytes such as PMN cells and other cell lines, will eventually replace the use of animals in elucidating the roles of these cytokines in response to microbe-derived cell damage. It will also be possible to use defensins as biomarkers to correlate failure in host cell defence systems with peptide heterogeneity.

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