Of the nature of the antigen

Abstract

A number of skin and conjunctival reactions - such as Arthus' phenomenon and the tuberculin test -are based on this condition of hypersensibility and prove valuable tests for the antigenic properties of substances. These results are specific. The injection of streptococci does not give rise to sera agglutinating staphylococci; here however there is an obvious morphological difference. But the injection of, or infection with, B.Faratyphosus B. does not give rise to sera agglutinating B. Paratyphosus A.; but the two bacilli are morphologically indistinguishable and biologically very similar. Passive or active immunity for the one does not, however, confer any immunity for the other. The symptoms of infection are different, the toxins are therefore different. Immune sera were found to be capable of distinguishing further than this. The clinical pictures of epidemic cerebro-spinal fever due to any of the causative cocci are identical but four strains can be distinguished by agglutinating sera (Gordon 1907). These questions then arise. Are the toxins producing the symptoms of the disease or anaphylaxis identical with the "antigen"? Is it possible to remove the antigenic principal from, the body a bacterium, or other antigenic material? Finally, to what class of substances do antigens belong? The distinction between the antigenic products isolated from bacteria and from other parasites, from blood and other tissues, has been almost entirely based on relative solubility in different solvents. It has become customary to regard the fractions extracted by physiological saline and similar solvents as 'protein"; and those isolated by organic solvents, principally ether and alcohol, 'as "lipoids and fats". This - 3 - division, though questionable from the chemical standpoint, gives an initial grouping of antigens. It is so far unquestioned that the proteins are antigenic. Crystallised egg albumen will give rise to antibodies, Dakin and Dale (1919) have shown that whilst by chemical and physical means it is not yet possible to distinguish between the crystallised egg albumen of the hen and the duck; antigenically they are specific in action. Further, that on racemization of these compounds different pro-portions were obtained of the laevao- and dextro- forms of certain of the constituent amino-acids. In this case then, protein specificity is associated with differences of stereo-chemical configuration. Bierry, Henri and Pettit Auguste (1904) stated that the "Nucleo-proteins" - that portion of different organs of a dog which was soluble in 0.2 % sodium carbonate and precipitated by acetic acid - when injected intraperitoneally into rabbits gave rise, in the serum of these rabbits, to products which were toxic for the organ from which they were prepared. Hence the serum of a rabbit inoculated with the nucleo-protein from dog's kidney when injected into a dog caused albuminuria. (1916) stated that the extracts of tissues with boiling water, yielding solutions of (2-nucleo-proteins gave rise to anaphylactic reactions but that the extracts from the pancreas of the pig and the ox and the spleen of the latter showed no specificity. Gideon Wells (1913) considered that the nucleic acids showed little evidence of antigenic properties; and that the so-called nucleo-proteins were mixtures of all kinds, both from the cytologist's nucleus and from the cytoplasm, probably in part denaturised and capable of giving rise to non-specific precipitins and complement fixation, even when they have lost the power of inducing anaphylactic reactions. Apart from tissue extracts and such special antigens as Cobra venom and ricin, antigens may be placed in three classes. First, the haemolytic antigens, those which confer haemolytic properties on the serum. Secondly, bacterial antigens, those which are intimately connected with the problems of disease. Thirdly, other parasitic antigens which may be closely parallel with the processes of infection, as is hydatid fluid in tests for hydatid disease; or purely empirical, as is the extract of ox heart in the Wassermann reaction. The chemical nature of the antigenic substances in all three classes may ultimately prove the same; nevertheless it is convenient to consider them separately although the second and third classes at least are comparable in many respects. (Abstract shortened by ProQuest.)