IMMUNIZATION TO BLOOD-GROUP ANTIGENS
a. Within a few months after birth, an infant makes anti-A and/or anti-B, if lacking
those antigens on its RBCs. Such antibodies are termed naturally occurring since they
have no apparent antigenic stimulus. Experiments in chicks have shown that these
antibodies probably develop as a result of exposure to bacterial antigens, closely
related chemically to blood group antigens (for example, Escherichia coli has an antigen
on its membrane closely resembling human B antigen). Naturally occurring antibodies
to antigens other than ABO are also often encountered, particularly in the I, Lewis, P,
and MN systems. These antibodies are usually lgM and react better at lower
b. Immune antibodies to blood group antigens usually develop as a result of
pregnancy, transfusion, or immunization (intential sensitization). Following
immunization, lgM antibodies are often seen first, followed by lgG antibodies, which
often predominate. These antibodies usually react better at 37C.
c. Antibodies other than anti-A or anti-B are usually called "irregular", "atypical",
or "unexpected" antibodies. The preferred term is unexpected.
d. There is extensive evidence in animals, such as mice, that the immune
response is genetically controlled (by the so-called Ir genes). It has been suggested
that this may apply in man also. Studies in man on the immune response to the Rh (D)
antigen indicate that approximately 30 percent of the Rho(D)-negative individuals
appear to be incapable of forming anti-Rho(D) even after repeated and/or large
transfusions of Rho(D)-positive blood. The antibody response in individuals who do
make antibody will depend on many factors, including the relative potency of the
antigen, the route of immunization, and the amount of blood given.
ANTIBODY STRUCTURE, FUNCTION, AND PROPERTIES
a. Plasma proteins with antibody activity are called immunoglobulins (lg).
During the last ten years, great advances have been made in defining their structure,
physiochemical properties, antigenic characteristics, serologic behavior, and biological
b. Each immunoglobulin molecule consists of basic units, each composed of
four polypeptide chains, two light chains (L) and two heavy chains (H), held together by
covalent disulfide bonds (S-S), and noncovalent interactions (see figure 1-2).
c. Five classes of immunoglobulins have been recognized on the basis of
antigenic differences in the heavy chain: lgG, lgA, lgM, lgD, and lgE (see figure 1-3). No
blood groups antibodies have yet been found to be lgD or lgE. There are two types of
light chains (kappa chain and lambda chain), which are common to, and found in, all
five immunoglobulin classes, but each individual immunoglobulin molecule has only one
type of light chain. Approximately 66 percent of the molecules of each class have
kappa light chains, and 33 percent have lambda light chains.