EVALUATION OF PLASMA ALPHA-2-MACROGLOBULIN AND INTERACTIONS WITH TUMOR-NECROSIS-FACTOR-ALPHA IN HORSES WITH ENDOTOXEMIC SIGNS

The electrophoretic position and behavior of the native and activated forms of equine plasma alpha-2-macroglobulin (alpha(2)M) were characte rized and compared to human alpha(2)M by nondenaturing polyacrylamide- gel electrophoresis (PAGE). Plasma alpha(2)M was also compared between 6 normal horses and 6 horses with clinical signs of colic and endotox emia due to volvulus or enteritis. Native and activated forms of alpha (2)M were quantified by PAGE and densitometry. Binding of radio-labele d recombinant human tumour necrosis factor-alpha (I-125-rhTNF-alpha) t o native and activated forms of equine alpha(2)M was also evaluated by autoradiography and densitometry of PAGE. Equine plasma alpha(2)M mig rated as a single band at a position equivalent to native human alpha( 2)M. Methylamine-reacted equine plasma samples resulted in faster migr ation of alpha(2)M in a similar position to activated human alpha(2)M. However, in methylamine-reacted equine plasma, an intermediate alpha( 2)M band was consistently present between the bands corresponding to n ative and activated alpha(2)M. Amounts of plasma alpha(2)M were simila r in normal and endotoxemic horses, and remained in the electrophoreti cally slow or unreacted native form. The vast majority of I-125-rHuTNF -alpha did not bind to alpha(2)M or other equine plasma proteins. I-12 5-rHuTNF-alpha bound weakly to both native and fast methylamine-reacte d equine forms of alpha(2)M, although binding was better to the activa ted form. This study indicates that: (1) equine plasma alpha(2)M behav es similarly to human alpha(2)M on PAGE, (2) plasma alpha(2)M of horse s can be activated to electrophoretically fast forms, but it is neithe r activated nor depleted during endotoxemia, and (3) the binding inter actions between equine alpha(2)M and TNF-alpha are too low to implicat e equine alpha(2)M as a regulator of TNF-alpha during endotoxemia in h orses.