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The recent burst of duplication and divergence of the bovine PLA2G2D genes is considered typical of immune response genes, and it was recently shown that PLA2G2D is abundantly expressed in mouse leukocytes and acts as an immunosuppressive phospholipase. Analysis of 1,143 Holstein bulls indicated that the four common haplotypes spanning PLA2G2D display copy number variation ranging from 1 to 4 per haploid genome. Association of the fourth haplotype with negative total merit remained significant (P < 0.002) when corrected for population relatedness. We compared the lipase and bactericidal activities of bovine pancreatic PLA2G1B with human PLA2G2A and G2D and bovine PLA2G2D1 and G2D4 proteins, which had been subcloned, expressed, and refolded by us, and the impact of point mutations in the calcium binding site was investigated. All tested phospholipases were ineffective bactericides of Escherichia coli isolated from bovine mastitis. However, in lactating mice treated with E. coli or lipopolysaccharide (LPS), intramammary injection of bovine PLA2G1B relieved visual and histological inflammation and reduced blood levels of infiltrating lactose. Further studies are warranted to determine whether the observed anti-inflammatory effect involves competitive binding of the receptor Pla2r1 which may mimic the LPS resistance effect in Pla2r1-deficient mice.

The enzyme catalase is well-known to catalyze the disintegration of hydrogen peroxide to water and oxygen; however, this study shows that its main function in bovine milk is oxidation of nitrite to nitrate. This process depends on hydrogen peroxide, of which the main source appears to be hydrogen peroxide formation that is coupled to the conversion of purines--xanthine in the present study--to uric acid by milk xanthine oxidase. However, additional secondary sources of hydrogen peroxide appear to be important during the relatively long storage of milk in the gland cistern. This paper demonstrates that the oxidation of nitrite to nitrate is necessary to prevent accumulation of free radicals and oxidative products during storage of milk in the gland and during the unavoidable delay between milking and pasteurization in dairy plants. Recommendations for minimizing the deterioration in milk quality during commercial storage are presented.