Intravascular hemolysis is mediated by: September 2007

Ans. D: IgG In a transfusion reaction or in alloimmune hemolytic anemia antibody mediated lysis of red blood cells involves triggering of the complement cascade. Some microbes form substances called hemolysins that have the specific action of destroying red blood cells; beta-hemolytic streptococci are an example. Intravenous administration of a hypotonic solution or plain distilled water will cause the red cells to fill with fluid until their membranes rupture and the cells are destroyed. Wherever either in vitro or in vivo IgG or IgM antibodies are bound to red blood cell antigens in the presence of complement, the complement cascade is triggered the final products of which include enzymes that result in holes being 'punched' in the wall of the red blood cell, allowing hemoglobin to escape and which is observed as lysis. Snake venoms and ceain plant substances may cause hemolysis. A great variety of chemical agents can lead to destruction of erythrocytes if there is exposure to a sufficiently high concentration of the substance. These chemical hemolytics include copper. Disorder of the immune response in which antibodies are made to 'self' red blood cell antigens resulting in the lysis of the cells (autoimmune hemolytic anemia)