12. IMMUNOLOGY OF FISH
469
thesizing cells provides the embryologist with challenging material for
consideration. Fourth, the phylogeny and progressive evolution of this
highly evolved response are still far from understood.
The purpose of this section is to provide a general concept from the
work on mammalian antibodies, especially human, and to show how the
study of fishes is assisting in enlarging this concept which is in a state
of rapid evolution.
A. The Immunoglobulins
Intensive work by the family of researchers, whose naincs and literature citations are to be found through the references cited below and in
the Introduction, has established the following general picture of the
nature of antibodies found in human and other serums. This picture
is well presented in considerable detail and with particular concern
for evolutionary considerations in a reccnt review by Putnam (1969).
The antibodirs are distinguished as a class from other proteins found
in blood, such as the estcrases, transferins, haptoglobulins, albumins,
and hemoglobins, through the physicochemical characteristics that associate them with the inimunoglobulins, iis is recognizcd by the name of
this class of protcins. Writers generally note that while antibodies are
all immunoglobulins (often abbreviated as Ig), it is difficult to prove
that all Ig are antibodies; however, this point docs not present significant difficulties in the considerations here. It will become apparent
as we proceed that the outstanding and unique feature of Ig is the
great heterogeneity of structure that is superimposed on the class
characteristics of these molecules. These characteristics include such
attributes as relative electrophoretic mobility and precipitability in contrast with other proteins in blood.
Early confusions in the nomenclature of the Ig and their molecular subunits have been largely resolved through international agreement ( cf. Putnam, 1969) and this nomenclature will be used here. Four major classes
( isotypes ) of Ig are distinguishable by their molecular weights, antigenic
spccificities, biological and other properties. These are tcmied, reslwctively, IgG or ,G, IgA or ,A, 1gh.I or ,M, and IgD or yD. Of thcse, &
and 7M are so much the best known that attention will be confincd to
them; ,G is a protein with a molecular wcight around 160,000, in contrast
with ,M with a molecular weight of about 1 0 . The differential sedimcmtation of these two molcculcs in tlw ultracentrifuge has oftcw led to
their being referred to as the 7 S and 19 S antibodies, respcctivcly. Physicochemical and physiological dissections ( through the study of Bcmce-
469
thesizing cells provides the embryologist with challenging material for
consideration. Fourth, the phylogeny and progressive evolution of this
highly evolved response are still far from understood.
The purpose of this section is to provide a general concept from the
work on mammalian antibodies, especially human, and to show how the
study of fishes is assisting in enlarging this concept which is in a state
of rapid evolution.
A. The Immunoglobulins
Intensive work by the family of researchers, whose naincs and literature citations are to be found through the references cited below and in
the Introduction, has established the following general picture of the
nature of antibodies found in human and other serums. This picture
is well presented in considerable detail and with particular concern
for evolutionary considerations in a reccnt review by Putnam (1969).
The antibodirs are distinguished as a class from other proteins found
in blood, such as the estcrases, transferins, haptoglobulins, albumins,
and hemoglobins, through the physicochemical characteristics that associate them with the inimunoglobulins, iis is recognizcd by the name of
this class of protcins. Writers generally note that while antibodies are
all immunoglobulins (often abbreviated as Ig), it is difficult to prove
that all Ig are antibodies; however, this point docs not present significant difficulties in the considerations here. It will become apparent
as we proceed that the outstanding and unique feature of Ig is the
great heterogeneity of structure that is superimposed on the class
characteristics of these molecules. These characteristics include such
attributes as relative electrophoretic mobility and precipitability in contrast with other proteins in blood.
Early confusions in the nomenclature of the Ig and their molecular subunits have been largely resolved through international agreement ( cf. Putnam, 1969) and this nomenclature will be used here. Four major classes
( isotypes ) of Ig are distinguishable by their molecular weights, antigenic
spccificities, biological and other properties. These are tcmied, reslwctively, IgG or ,G, IgA or ,A, 1gh.I or ,M, and IgD or yD. Of thcse, &
and 7M are so much the best known that attention will be confincd to
them; ,G is a protein with a molecular wcight around 160,000, in contrast
with ,M with a molecular weight of about 1 0 . The differential sedimcmtation of these two molcculcs in tlw ultracentrifuge has oftcw led to
their being referred to as the 7 S and 19 S antibodies, respcctivcly. Physicochemical and physiological dissections ( through the study of Bcmce-