Isolation and characterization of the eighth component of the bovine complement system

Marilyn Menger From the Department of Microbiology and Immunology, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada K7L 3N6.

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Richard D. Sowery From the Department of Microbiology and Immunology, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada K7L 3N6.

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W. Peter Aston From the Department of Microbiology and Immunology, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada K7L 3N6.

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Abstract

Objective

To isolate and characterize the eighth component of the complement system (C8) in cattle.

Sample Population

Fresh plasma obtained from beef cattle.

Procedures

Plasma samples were fractionated, using sequential precipitation and ion-exchange and gel-filtration chromatography, to yield C8. The protein was identified throughout the procedure on the basis of its hemolytic function. Electrophoresis in polyacrylamide gels was used to determine molecular weight and composition of polypeptide chains. Reconstitution of classical and alternative complement pathways was used to characterize the hemolytic function of bovine C8.

Results

The bovine C8 protein consisted of a disulfide-bonded α-γ heterodimer that was noncovalently associated with a β chain. Apparent molecular weight of the α, β, and γ chains under reducing conditions were 66, 61, and 23 kd, respectively. In the classical pathway of activation, bovine C8 and the ninth component of the complement system (C9) had species incompatibility with human C8 and C9 on sheep erythrocyte target cells.

Conclusions

A simple 4-step fractionation procedure provided good yield of bovine C8 from plasma. The isolated protein was structurally comparable to C8 from other species. Purified bovine C8 may be useful in functional hemolytic assays to investigate the roles of complement-mediated lysis in the pathogenesis of inflammatory diseases and the killing of susceptible microorganisms. (Am J Vet Res 1999;60:1474–1477)

Abstract

Objective

To isolate and characterize the eighth component of the complement system (C8) in cattle.

Sample Population

Fresh plasma obtained from beef cattle.

Procedures

Plasma samples were fractionated, using sequential precipitation and ion-exchange and gel-filtration chromatography, to yield C8. The protein was identified throughout the procedure on the basis of its hemolytic function. Electrophoresis in polyacrylamide gels was used to determine molecular weight and composition of polypeptide chains. Reconstitution of classical and alternative complement pathways was used to characterize the hemolytic function of bovine C8.

Results

The bovine C8 protein consisted of a disulfide-bonded α-γ heterodimer that was noncovalently associated with a β chain. Apparent molecular weight of the α, β, and γ chains under reducing conditions were 66, 61, and 23 kd, respectively. In the classical pathway of activation, bovine C8 and the ninth component of the complement system (C9) had species incompatibility with human C8 and C9 on sheep erythrocyte target cells.

Conclusions

A simple 4-step fractionation procedure provided good yield of bovine C8 from plasma. The isolated protein was structurally comparable to C8 from other species. Purified bovine C8 may be useful in functional hemolytic assays to investigate the roles of complement-mediated lysis in the pathogenesis of inflammatory diseases and the killing of susceptible microorganisms. (Am J Vet Res 1999;60:1474–1477)

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