A monoclonal-antibody-defined adhesion-related antigen on bovine neutrophils is required for neutrophil aggregation

Biosynthesis of B2-integrin, intracellular calcium signalling and functional responses of normal and CD18-deficient bovine neutrophils

1Biosynthesis of CD11/CD18 in bovine leucocytes, intracellular Ca2+ ([Ca2+]i) signalling, chemiluminescent responses and membrane fluidity of neutrophils and the effects of D-mannose on neutrophils from control heifers and a heifer with bovine leucocyte adhesion deficiency (BLAD) were measured. The synthesis of CD11/CD18 complex was clearly detected in leucocytes from a normal heifer, but not in a BLAD-affected heifer. The transient phase of increased [Ca2+]i was clearly detected in neutrophils from a heifer with BLAD stimulated with opsonised zymosan, aggregated bovine immunoglobulin G or concanavalin A, whereas the sustained phase was deficient or significantly decreased compared with control heifers. [Ca2+]i signalling of neutrophils from control heifers and a heifer with BLAD stimulated with phorbol myristate acetate via an 11b/CD18-independent pathway showed no transient phase, and the subsequent increase in [Ca2+]i was almost identical in neutrophils from affected and control heifers. [Ca2+]i concentration and chemiluminescent responses of neutrophils from a control heifer were clearly decreased by treatment with anti-CD18 and anti-IgG antibodies. No differences in membrane fluidity were detected between neutrophils derived from control and CD18-deficient cattle. D-mannose binds mainly to Fc rather than CD18 receptors, and decreased Agg-IgG induced [Ca2+]i and the chemiluminescent response of neutrophils. The [Ca2+]i responses and Agg-IgG induced chemiluminescent responses of neutrophils from control heifers and a BLAD-affected heifer were inhibited by D-mannose. The characteristic changes of [Ca2+]i signalling and functional responses of B2-integrin-deficient neutrophils were demonstrated.

The effect of bovine seminal plasma on the function and integrity of bovine neutrophils

Spermatozoa, by virtue of their high content of polyunsaturated fatty acids and limited antioxidant activity, are highly sensitive to lipid peroxidation. Sources of reactive oxygen species in the female genital tract include neutrophils recruited in response to insemination or those contained within the ejaculate, or even spermatozoa themselves. This study was undertaken to investigate the effect of seminal plasma of bulls on bovine neutrophils. Seminal plasma was removed from ejaculates of 6 healthy bulls by centrifugation. Neutrophils were isolated from jugular venous blood samples obtained from lactating Holstein cows. Seminal plasma was found to decrease measured Superoxide anion production by activated neutrophils (P = 0.008) in a concentration-dependent manner over the range tested (0 to 16%). This effect may reflect Superoxide scavenging by the seminal plasma or direct inhibition of the neutrophils. It has the potential physiological advantage of protecting spermatozoa from oxidative damage. Seminal plasma was found to reduce homotypic neutrophil aggregation dramatically (P < 0.0001). At a seminal plasma concentration of 0.2% neutrophil aggregation was virtually abolished. Homotypic neutrophil aggregation depends on the CD 11b/CD 18 (Mac-1) receptor, which also functions as the C3bi receptor (known as complement receptor-3 or CR3). If this receptor is down-regulated, the ability of neutrophils to phagocytose complement-opsonized microorganisms would be compromised. Finally, seminal plasma was found to increase neutrophil permeability to trypan blue in a concentration and time dependent fashion (P < 0.0001), indicating a direct cytotoxic effect. Taken together, these findings indicate a profound inhibition of neutrophil function by bovine seminal plasma. While these mechanisms are likely to protect spermatozoa from oxidative damage or phagocytosis, they also have the potential to diminish defense against pathogenic microorganisms.

CD14 and tissue factor expression by bacterial lipopolysaccharide-stimulated bovine alveolar macrophages in vitro

The membrane-associated CD14 receptor (mCD14) is a monocyte/macrophage differentiation antigen, and it has been demonstrated to serve as a receptor for bacterial lipopolysaccharide (LPS; endotoxin). Binding of LPS to mCD14 has been shown to be associated with LPS-induced macrophage, monocyte, and neutrophil activation in humans. In this report, we describe the presence and function of an mCD14-like receptor on bovine alveolar macrophages (bAM). An immunofluorescence technique and flow cytometric analysis indicated binding of anti-human CD14 monoclonal antibodies (MAb) My4, 3C10, and 60bd to bAM. Binding of anti-CD14 MAb (3C10 and MY4) was reduced over 20% by pretreatment of bAM with phosphatidylinositol-specific phospholipase C (0.5 to 1.0 U/ml), indicating that bovine mCD14 is a glycosyl phosphatidylinositol-anchored protein. In addition, pretreatment of bAM with anti-CD14 MAb decreased binding of 125I-labeled LPS to macrophages, suggesting that bovine mCD14 serves as a receptor for LPS. A cDNA probe based on the human sequence for CD14 was used in Northern (RNA) blot analysis, and hybridization to human monocyte CD14 yielded the expected 1.5-kb band. Hybridization to bovine mRNA yielded a 1.5-kb band plus an unexpected 3.1-kb band. Constitutive expression of bovine CD14 mRNA was observed, and the expression level was modestly elevated in bAM stimulated for 24 h with LPS (1 ng/ml) in the presence of bovine serum. The function and activation of bAM were assessed by quantitation of tissue factor (TF) expression on the cells using an activated factor X-related chromogenic assay and S-2222 substrate. LPS (1 ng/ml)-mediated upregulation of TF expression on bAM was dependent on the presence of bovine serum components, and TF expression was inhibited by anti-CD14 MAb. In addition, TF mRNA levels in LPS-stimulated bAM were decreased by pretreatment of cells with anti-CD14 MAb (MAb 60bd, 10 micrograms/ml).