To study the effects of loxosceles laeta
venom on red blood cells and the possible factors involved in
hemolysis during
arachnidism, in vitro models were designed to measure the role of
loxosceles venom,
calcium,
complement and
antibodies in the mechanism of red blood cell destruction. The degree of basal
hemolysis was measured in a 5%
suspension of group O, Rh (+) red blood cells in pH 7.4
buffer. In a similar
suspension spider venom was added in amounts equivalent to one
venom gland. After 72 hours of incubation, basal
hemolysis was 5.59 +/- 2.04% which increased to 26.01 +/- 7.9% adding
venom (p < 0.001). Adding
calcium to the incubation medium,
hemolysis increased to 88.5 +/- 7.16% (p < 0.001). Incubating red blood cells with control human serum and
venom,
hemolysis was 14.58 +/- 2.42%, which decreased significantly to 6.85 +/- 3.35% when serum was heat inactivated; this demonstrates an effect of the presence of
complement. We did not find
antivenom antibody production in patients with
arachnidism 10, 15 or 30 days after the
spider bite. It is thus demonstrated that loxosceles laeta
venom has a direct lytic action on red blood cells that is
calcium and
complement dependent and is not mediated by
antibodies or other substance.