Masters Theses

Date of Award

6-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Stephen P. Oliver

Committee Members

James D. Godkin, Bert H. Erickson

Abstract

Effects of bovine mammary secretions obtained at various stages of the lactation cycle on bovine peripheral blood mononuclear cell blastogenesis were evaluated in Part II using concanavalin A and phytohemagglutinin as mitogens. In Part III, response of blood mononuclear cells to mitogens throughout the dry period was determined at drying off, 14-16 and 28-30 d post drying off, 14-12 d prior to parturition and at parturition. Concanavalin A, phytohemagglutinin, and Escherichia coli 0111:84 lipopolysaccharide were used as mitogens. Effects of fractionated and whole mammary secretion whey on bovine peripheral blood mononuclear cell blastogenesis were determined in Part IV. Concanavalin A and phytohemagglutinin were used as mitogens. Mammary secretions were collected from four cows 16-2 d prior to parturition and fractionated by gel filtration chromatography. In all studies, mononuclear cells were isolated from bovine blood by density gradient centrifugation. Mononuclear cell blastogenesis was evaluated by methyl-³H-thymidine incorporation. In Part II, all secretions markedly inhibited mononuclear cell blastogenesis compared to stimulated controls. Normal milk caused the least inhibition of blastogenesis. Colostrum and secretions obtained 7 d post drying off were associated with greatest inhibition of mononuclear cell blastogenesis. Mammary secretion wheys caused greater inhibition than mammary secretion skims. Phytohemagglutinin-stimulated cell blastogenesis was less suppressed by mammary secretions than concanavalin A-stimulated blastogenesis. In Part III, stimulation of mononuclear cells by concanavalin A increased slightly through 28 d post drying off then decreased to its lowest point at parturition. Phytohemagglutinin-induced blastogenesis decreased consistently throughout involution and was lowest at parturition. Lipopolysaccharide-induced blastogenesis increased from drying off to mid-dry period. However, due to lack of mononuclear cell response to lipopolysaccharide compared to concanavalin A and phytohemagglutinin, use of lipopolysaccharide was discontinued. Mammary secretion whey collected 16-2 d prior to parturition markedly depressed the response of peripheral blood mononuclear cells to mitogens in Part IV. Mammary secretion whey eluted from column chromatography in four major groups designated protein peaks 1, 2, 3 and 4. Concanavalin A-stimulated mononuclear cell blastogenesis was most inhibited by concentrated preparations of protein peak 1. Phytohemagglutininstimulated mononuclear cell blastogenesis was most inhibited by concentrated preparations of protein peak 2. Unconcentrated protein peak 2 was associated with greatest inhibition of both concanavalin A- and phytohemagglutinin-stimulated mononuclear cell blastogenesis. Protein peaks 3 and 4 inhibited mononuclear cell blastogenesis to a lesser degree than protein peak 2. Phytohemagglutinin-stimulated cells were less inhibited by both whole and fractionated mammary secretion whey than concanavalin A stimulated cells. Insensitivity of phytohemagglutinin-stimulated cells compared to concanavalin A-stimulated cells to blastogenic inhibition by mammary secretions in Part II and fractionated and whole mammary secretion whey in Part IV may reflect different subpopulations of T-lymphocytes in bovine blood. Variation in response of mononuclear cells to conca-navalin A and phytohemagglutinin throughout involution in Part III may also support this hypothesis. Results of Part II indicated that mammary secretions collected during physiological transitions of the mammary gland were most inhibitory to bovine peripheral blood mononuclear cell blastogenesis. Suppression of mitogen-induced mononuclear cell blastogenesis at parturition observed in Part III may have been caused by hormones and other factors associated with impending parturition and lactation. Variation in inhibition of concanavalin A- and phytohemagglutinin-induced mononuclear cell blastogenesis by whey fractions in Part IV may reflect different immunosuppressants in mammary secretions with different specificities for subpopulations of cells stimulated by concanavalin A and phytohemagglutinin. Bovine mammary gland mononuclear cells are derived from peripheral blood. Suppression of mononuclear cell blastogenesis by mammary secretions in the gland may contribute to observed variation in rates of new intramammary infection during involution, especially during physiological transitions of the gland.

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