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hemolysis 317 hemolytic plaque assay
hemolysis
Interruption of the cellular integrity of red blood cells that
may be immune- or nonimmune-mediated. Clinically,
immune hemolysis may be IgM-mediated when immunoglobulins
combine with red blood cell surfaces for which
they are specific, such as the ABO blood groups, and
activate complement to produce lysis. This results in the
release of free hemoglobin in the intravascular space with
serious consequences. By contrast, hemolysis mediated by
IgG in the extravascular space may be less severe. Indirect
bilirubin is elevated, as the liver may not be able to conjugate
the bilirubin in case of massive hemolysis. Lactate
dehydrogenase is elevated, and hemoglobin appears in the
blood and urine. Urobilinogen is elevated in both urine and
feces. Hemolysis may be also attributable to the action of
enzymes or other chemicals on cell membranes. It can also
be induced by such mechanisms as placing the red cells in a
hypotonic solution.
hemolytic anemia
A disease characterized by diminished circulating erythrocytes
as a consequence of their destruction based either
on an intrinsic abnormality, as in sickle cell anemia and
thalassemia, or as a consequence of membrane-specific
antibody and complement (Type II hypersensitivity).
Certain infections such as malaria are also associated with
hemolytic anemia. Free hemoglobin in serum may lead to
renal problems.
hemolytic anemia of the newborn
Refer to hemolytic disease of the newborn.
hemolytic disease of the newborn (HDN)
A fetus with RhD + red blood cells can stimulate an RhD –
mother to produce anti-RhD immunoglobulin G (IgG)
antibodies that cross the placenta and destroy the fetal
red blood cells when a sufficient titer is obtained. This is
usually not until the third pregnancy with an Rh + fetus. At
parturition, the RhD + red blood cells enter the maternal
(1) First Pregnancy (Initial Sensitization)
RBC with RhD antigen
Maternal circulation
Placenta
Mother
B
Memory cell
Hemolysis
circulation and subsequent pregnancies provide a booster to
this response. With the third pregnancy, a sufficient quantity
of high-titer antibody crosses the placenta to produce
considerable lysis of fetal red blood cells. This may lead to
erythroblastosis fetalis (hemolytic disease of the newborn).
Seventy percent of HDN cases are due to RhD incompatibility
of the mother and fetus. Exchange transfusions may
be required for treatment. Two other antibodies against
erythrocytes that may likewise be a cause for transfusion
exchange include anti-Fy a and Kell. As bilirubin levels
rise, the immature blood–brain barrier permits bilirubin to
penetrate and deposit on the basal ganglia. Anti-D antibody
passively injected into the mother following parturition
unites with the RhD + red cells, leading to their elimination
by the mononuclear phagocyte system. Also termed erythroblastosis
fetalis.
hemolytic plaque assay
A technique to identify and enumerate cells synthesizing
antibodies. Typically, spleen cells from a mouse
immunized against sheep red blood cells are combined
with melted agar or agarose in which sheep erythrocytes
are suspended. After gentle mixing, the suspension is
distributed into Petri plates, where it gels. This is followed
by incubation at 37°C, after which complement is added
to the dish from a pipette. Thus, the sheep erythrocytes
(SRBCs) surrounding cells secreting immunoglobulin M
(IgM) antibody against SRBCs are lysed by the added
complement, producing a clear zone of hemolysis resembling
the effect produced by β hemolytic streptococci on
blood agar. IgG antibody against sheep erythrocytes can
be identified by adding anti-IgG antibody to aid lysis by
complement. Whereas modifications of this method have
been used to identify cells producing antibodies against a
variety of antigens or haptens conjugated to the sheep red
cells, it can also be used to ascertain the immunoglobulin
class secreted. Refer to figure for Jerne plaque assay.
(2) Second and Third Pregnancies (2° and 3° Sensitizations)
IgG
Representation of the mechanism of hemolytic disease of the newborn.
+C
+C
B
Memory cell
Plasma cell
H