Ivanovsky, Dmitri Iosifovich WORLD OF MICROBIOLOGY AND IMMUNOLOGY316•
the body as an antibody. The antigen-binding capacity of an
immunoglobulin is related to the three-dimensional shape of
the molecule. Immunoglobulin isotype and allotype deter-
mines the diversity in shape of immunoglobulins.
Immunoglobulins are structured with two Y-shaped
“heavy” chains. To each of these a shorter “light” chain is
linked. Within each chain there are regions whose amino acid
sequence remains constant from immunoglobulin to
immunoglobulin. There are also regions whose amino acid
sequence is somewhat different and markedly different
between the myriad of immunoglobulins that can be made.
The type of heavy chain an immunoglobulin has deter-
mines the isotype. Immunoglobulins of the same isotype have
the same amino acid structure in two specific regions of the
heavy chain. The similarity in amino acid sequence extends to
the three-dimensional structure that the immunoglobulin
adopts. Thus, immunoglobulins of the same isotype have sim-
ilar shapes and so similar antigen binding characteristics. The
different classes and subclasses of antibody protein arising
from the amino acid variations represent the different isotypes.
In humans, there are five immunoglobulin isotypes:
IgA, IgD, IgG, IgE, and IgM. All humans whose immune sys-
tem is functioning correctly possess all these isotypes. Thus,
no antigenic response would be elicited if an IgA from one
person was injected into another.
Immunoglobulins can also be classified by their so-
called allotypes. Allotypes are also determined by the amino
acid sequences of the heavy and light chains. Allotypes focus
on the variable regions of the chains. By their variable nature,
differences in the amino acid sequence can exist even between
members of the same species. Allotypes represent what is
termed polymorphisms within certain heavy or light chains.
Not all members of a species such as man possess any
particular allotype. In contrast to isotypes, the injection of a
specific allotype from one person into another could elicit an
antigenic reaction in the recipient.See also Antibody-antigen, biochemical and molecular
reactionsIVANOVSKY, DMITRIIOSIFOVICH
(1864-1920)Ivanovsky, Dmitri Iosifovich
Russian botanistDmitri Ivanovsky, in studying a disease that affects tobacco
plants, paved the way for the discovery of the infectious parti-
cle known as a virus.
Ivanovsky, the son of a landowner, was born in Gdov,
Russia. He attended the Gymnasium of Gdov and later grad-
uated as a gold medalist from the Gymnasium of St.
Petersburg in 1883. At the University of St. Petersburg, he
enrolled in the natural science department and studied under
several prominent Russian scientists. While a student, he
became interested in diseases that destroy tobacco plants. He
graduated in 1888 after presenting his thesis On Two Diseases
of Tobacco Plants.
The following year, he was asked by the directors of
the Department of Agriculture to study a new tobacco dis-
ease, called tobacco mosaic, that had afflicted plants in the
Crimean region. He crushed the infected leaves, which were
distinguished by their mosaic pattern, into sap and then
forced the material through a Chamberland bacterial filter
that was known to remove all bacteria. Despite following
this procedure, the sap, when brushed on the leaves of
healthy plants, was still toxic enough to cause disease.
Ivanovsky’s 1892 report on the tobacco mosaic disease
detailed what he maintained must be an agent smaller than
bacteria. It was the first study in which factual evidence was
offered concerning the existence of this new kind of infec-
tious pathogen.
Ivanovsky’s work was ignored by the scientific commu-
nity, and he eventually abandoned his study of this pathogen
without understanding the implications of his research. The
Dutch botanist, Martinus Willem Beijerinck, repeated
Ivanovsky’s experiments with this new pathogenic source,
giving it the name filterable virus in 1898.See alsoTobacco mosaic virus (TMV); Virologywomi_I 5/6/03 3:23 PM Page 316