J.t is well established thait both the an ti body deficiency and the reaction beru,een antigen and _ant.i hody cause many diseases Then there is antibody ·c1e,ficiency the resulting disease is called antibody deficiency disease; and when the contact of antigen vih antibody produces the disease or the complex of antigen with antibody precipitates and causes tissue damage the ,lesion is called hypersensitivity disease. These two groups 01[ diseases are coI!ectively called immunologic dise ses. The deficiency group is brought about by paucity or absence of B lymphocytes and T lymphocytes. This absence is either congenital or acquired. The list of the diseases resulted from this de:icicncy is given.
The next group; the hypersensitivity diseases; are divided into four categories; according to ·the mechanism by which arc produced.
THE FIRST TYPE; are the diseases which are produced by anaphylactic type of reaction. The best example of these arc : allergic asthma, allergic thinitis and angioneurntic edema. There is release of vasoc-tive substances from the ma;;t cells and platelet,; and this release is due to the contact of antigen with IgE which is :fixed on the surface of the target cells rspecial'ly the rnastocytes. These diseases can he recognized by skin tests.
THF SECOND TYPE; arc the diseases resulted from cytolysis and inactivation. Cytolysis 1s exampli-:fied by red cells, white cells and pla,telets destructicn; and inactivation relates to insulip, intrinsic far.tor and coagulation factors, so by this mechanism many disPases such as hemolytic anemia, thromhocytopeni:1. and leukopenia as well as diabetes mdlitus, pernicious anemia and coagulation defects arc produced. We can diagnose these diseases by Coombs tests and immunofluorescent technices. THE THIRD TY.PE : is the type of diseases which arc produced by the combination o·f antigen and antibody; so called the toxic complex. This complex is ,precipitated in the tissues and causes many diseases such as systemic lupus crythematosus, rheumatoid 2 rthritis polyarter,itis nodosa ancl glomeruloncphritis. There are diHercnt methods and tests to diagnose these diseases; namely the complement fixation te:t, the immunotluorescent tests, detection oantinuclear factors and L.E. cells as ,veil as tissue examinations.
THE FOURT,H TYPE: represents the diseases brought about by the reaction betveen sensitized lymphocytes and the .functioning cells of all organs. These diseases are best cxamplified by autoimmune thyroidities, orchitis, parotitis derrnatomyositis and scelcro-dcrma. This mechanism is be1i.eficial in the .fight o; the immune system against cancer cells. This type of reaction can be rcognized by immunofluorcsccnt technics, tuberculin test and tissue biopsies.