Bovine natural killer activity against virally infected cells inhibited by monoclonal antibodies

NKp46 defines a subset of bovine leukocytes with natural killer cell characteristics

Natural killer (NK) cells have not previously been precisely identified or characterized in cattle or any other ruminant species. We have generated a monoclonal antibody against bovine NKp46, which is expressed exclusively by NK cells in man. NKp46+ cells comprised 1-10% of blood mononuclear cells in cattle, and did not stain with antibodies against CD3, CD4, TCR1, B cell or granulocyte markers. The majority of the NKp46+ cells expressed CD2, and a variable fraction also expressed CD8. The tissue distribution of NKp46+ cells in cattle was compatible with the tissue distribution of NK cells in other species. Bovine NKp46+ cells had typical, large granular lymphocyte morphology, and proliferated vigorously in response to bovine IL-2 for a limited number of cell divisions. IL-2-activated NKp46+ cells killed the bovine kidney cell line MDBK. This cytotoxicity was inhibited by preincubation with antibody against NKp46. In a redirected lysis assay, IL-2-activated NKp46+ cells killed the FcgammaR+ target cell line P815 after preincubation with antibody against NKp46. Together, these data indicate that bovine NKp46 is anactivating receptor and demonstrate the existence of a subset of leukocytes in cattle that, in terms of surface markers, morphology and function, represent NK cells.

Effects of purified bovine whey factors on cellular immune functions in ruminants

The immunomodulatory properties of bovine milk and whey have long been documented. The recent advance of whey protein fractionation technology has now allowed us to study the immunobiological properties of some highly purified components of whey, with a view to exploiting their possible industrial and biomedical applications. The effects of fractionated bovine whey proteins on cellular immune responses were therefore examined using a panel of in vitro assays. Both lactoferrin (LF) and lactoperoxidase (LP) were found to inhibit proliferation and interferon-gamma (IFN-gamma) production of ovine blood lymphocytes in response to mitogenic stimulation. However, their effects in a combined fraction or in whey protein concentrate (WPC) were either diminished or eliminated. LF and LP had no effect on lipopolysaccharide (LPS)-induced ovine blood lymphocyte proliferation, production of interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF alpha) by ovine bronchoalveolar lavage (BAL) macrophages, major histocompatibility complex (MHC) Class II antigen expression by ovine BAL macrophages and bovine natural killer (NK) cell activity. However, alpha-lactalbumin (alpha LA) exhibited an enhancing effect on IL-1 beta production. It is noteworthy that as bovine whey fractions become progressively more purified, their modulatory effects on the immune response also become more clear-cut. The effects of LF, LP and alpha LA may be eliminated by their combination in whey or by other minor components of whey. Further investigation of industrial applications for whey proteins of high purity is warranted.

Modulation of immune responses by bovine beta-casein

The present reports the influence of bovine beta-casein on in vitro and in vivo immune responses. Bovine beta-casein showed an inhibitory effect on ovine neutrophil chemotaxis but had an enhancing effect on superoxide production by neutrophils. In response to mitogenic stimulation, the proliferative response of both T and B lymphocytes was significantly enhanced by beta-casein. While beta-casein had no significant effects on IFN gamma production by ovine blood lymphocytes, and TNF alpha production and MCH Class II antigen expression by ovine bronchoalveolar macrophages, it enhanced IL-1 beta production by the macrophages, beta-casein also had no influence on bovine NK cell activity against a virally-infected cell line. Interestingly, beta-casein was found to reduce the adjuvant effect of matrix immune stimulating complexes (ISCOM) on anti-ovalbumin antibody response in mice when given intramuscularly. Taken together, the results suggest that bovine beta-casein had selective modulating effects in vitro on both innate and adaptive immune responses in ruminants, whereas systemic administration of beta-casein, that might have a depressive effect on adjuvant activity, requires further study.

Identification of a monoclonal antibody reactive with the bovine orthologue of CD3 (BoCD3)

A monoclonal antibody (mAb), MM1A, that identifies a molecule expressed on a large percentage of bovine lymphocytes (60-80%) was examined to determine its specificity. Two and three colour immunofluorescence analysis using flow cytometry revealed the molecule is highly expressed on all CD4+ and CD8+ lymphocytes and lymphocytes that express WC1 and the gamma/delta TCR. In contrast to mAbs reactive with BoCD5, MM1A did not react with B lymphocytes. Biochemical analysis revealed that the mAb immunoprecipitates a molecular complex comprising a set of peptides with M(r) approximately 12, 16, 22, 32, 36, and 44 kDa under reducing conditions and an additional 96 kDa peptide complex under non-reducing conditions. The data indicate that MM1A recognizes the bovine orthologue of CD3 (BoCD3).