Antibodies are globulin proteins (immunoglobulins) that are
synthesized in serum and tissue fluids, which react specifically with the
antigen that stimulated their production. Three types of globulins are present
in the blood: alpha, beta, and gamma.
The antibodies are the gamma globulins. Antibodies are one of the
major plasma proteins, and against infection often referred to as “first line
of defense”. The most important func-tion of antibodies is to confer protection
against microbial pathogens. Antibodies confer protection in the following
They prevent attachment of microbes to mucosal surfaces of the
They reduce virulence of microbes by neutralizing toxins and
They facilitate phagocytosis by opsonization of microbes.
They activate complement, leading to complement-mediated activities
Behring and Kitasato performed the first experiments that proved the physical
existence of antibodies in 1890. They demonstrated that serum obtained from
rabbits immunized with tetanus or diphtheria toxins could prevent disease in
mice infected with such pathogens. The unknown substance that was present in
serum and that provided protection on transfer was named “antitoxin” by Tizzoni
and Cattani in 1891. Subsequently, experimental works by Paul Ehrlich and Jules
Bordet demonstrated that a protective response could be generated even against
whole cells (erythrocytes). The more inclusive term antibody subsequently replaced the term antitoxin.
and Kabat accomplished the first successful attempt to identify antibody
molecules in 1939. They demon-strated that hyperimmunization increased the
concentration of -globulins in serum and that this fraction contained anti-body
activity. Because -globulins are large-molecular-weight proteins, it was
suggested that further characterization of anti-bodies requires breaking them
into smaller and easily handled fragments.
in 1959, succeeded in digesting rabbit immunoglobu-lin G (IgG) with the
proteolytic enzyme papain. These produced two distinct fragments: a monovalent
fragment with antigen-binding activity, termed Fab (fragment antigen binding)
and a second fragment that retained the antibody’s effector functions and
crystallized readily into a lattice, termed Fc (fragment crys-tallizable).
Edelman and Poulik using a similar method splitted myeloma globulins into two
distinct components, which subse-quently were termed heavy (H) and light (L)
World Health Organization (WHO) in 1964 coined the term “immunoglobulin (Ig)”
for the term antibody. The immunoglobulin includes not only antibody globulins
but also the cryoglobulins, macroglobulins, and abnormal myeloma proteins.
Thus, all antibodies are immunoglobulins but not all immunoglobulins may be