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JOHN E. CUSHINC
which are widely distributed throughout the body, along the linings
of the circulatory system, and in the blood itself. These also gather at
foci of activity.
There is, therefore, a complex relation between phagocytic cells
which injest and digest antigen and those mediating specific immunity.
This relationship is not yet understood, but evidence is accumulating
to suggest that the phagocytes, after initial processing of antigen, transmit specific molecular information to the immunological system that
leads to the reactions of adaptive immunity.
A final point is that not all the immunologically competent cells
react following a given antigenic stimulus. The extent of reaction is determined in part by the geography of the stimulus in relation to the
cells involved, and in any case only a minority of available cells becomes
committed to a given response. There is a general concept that any
single cell and its descendents can produce only one kind of several
antibody types genetically available to it, but exceptions to this are
still being collated. While this point may not always be true, it does make
it easy to visualize the immunological system as consisting of a coexisting array of clones of lymphoidal cells capable of recognizing and
reacting to different ones among the total antigens that an individual
will be exposed to and of making one or another of the heterogeneous
immunglobulins reactive to the antigen involved.
The reader should be aware that the above discussion presents only
a very brief sketch of a very difficult research area. It is, for example,
easy to distinguish an array of cell types by their morphology, but it is
very difficult to determine their ontogenetic and physiological relationships and also to be certain that cells of the same appearance in one
species are homologous with those in another. The reader is recommended to read descriptions of experiments that are being performed
in this area, notably those showing the ingenuity of transplantation
researchers, who are able, for example, to “empty” mice of lymphocytes
of their own, replace them with genetically marked cells of other individuals in an array of combinations, and apply a battery of methods
available to the immunologist and histochemist in interpreting the results. One basically simple experiment, easily visualized, takes advantage
of an evolutionary “dissection” occurring in the chicken. This has been
the development of the distinctive organ called the “bursa of Fabricius”
along the lower gut of this species. Removal and transplantation of this
organ in various combinations with the thymus has contributed greatly
to the idea of two basic lymphoidal populations of cells, one producing
immunoglobulins mediated by the bursa of Fabricius, and one responsible
JOHN E. CUSHINC
which are widely distributed throughout the body, along the linings
of the circulatory system, and in the blood itself. These also gather at
foci of activity.
There is, therefore, a complex relation between phagocytic cells
which injest and digest antigen and those mediating specific immunity.
This relationship is not yet understood, but evidence is accumulating
to suggest that the phagocytes, after initial processing of antigen, transmit specific molecular information to the immunological system that
leads to the reactions of adaptive immunity.
A final point is that not all the immunologically competent cells
react following a given antigenic stimulus. The extent of reaction is determined in part by the geography of the stimulus in relation to the
cells involved, and in any case only a minority of available cells becomes
committed to a given response. There is a general concept that any
single cell and its descendents can produce only one kind of several
antibody types genetically available to it, but exceptions to this are
still being collated. While this point may not always be true, it does make
it easy to visualize the immunological system as consisting of a coexisting array of clones of lymphoidal cells capable of recognizing and
reacting to different ones among the total antigens that an individual
will be exposed to and of making one or another of the heterogeneous
immunglobulins reactive to the antigen involved.
The reader should be aware that the above discussion presents only
a very brief sketch of a very difficult research area. It is, for example,
easy to distinguish an array of cell types by their morphology, but it is
very difficult to determine their ontogenetic and physiological relationships and also to be certain that cells of the same appearance in one
species are homologous with those in another. The reader is recommended to read descriptions of experiments that are being performed
in this area, notably those showing the ingenuity of transplantation
researchers, who are able, for example, to “empty” mice of lymphocytes
of their own, replace them with genetically marked cells of other individuals in an array of combinations, and apply a battery of methods
available to the immunologist and histochemist in interpreting the results. One basically simple experiment, easily visualized, takes advantage
of an evolutionary “dissection” occurring in the chicken. This has been
the development of the distinctive organ called the “bursa of Fabricius”
along the lower gut of this species. Removal and transplantation of this
organ in various combinations with the thymus has contributed greatly
to the idea of two basic lymphoidal populations of cells, one producing
immunoglobulins mediated by the bursa of Fabricius, and one responsible