IMMUNOLOGIC DISEASE

IMMUNOLOGIC diseases are those in which some kind of immunologic sequence of events in the body is of prime importance in initiation and progression. Underlying this there may be an infectious or toxic process, or simply exposure to an antigenic substance or cell. The list of such diseases is fairly lengthy, and they are often all spoken of as diseases of allergy or hypersensitivity. The main purpose of this paper is to categorize these diseases, as well as facts and speculation permit, on the basis of underlying immunologic mechanisms; the intention is to dispel the notion that these are all necessarily products of those changes which the term "hypersensitivity" denotes. It is worth while to bring precision to our semantics because otherwise we may easily be trapped into an assumption of knowledge which we do not have, and into a corollary tendency to stop delving into that which we think we already know. The term "hypersensitivity" implies certain fairly well-understood immunologic processes which account for some of the diseases to be mentioned, but from the mechanistic standpoint these processes do not explain other disorders which may nonetheless be of immunologic origin. The roster of these diseases includes such unequivocally allergic conditions as asthma, hay fever, serum sickness, and anaphylaxis, as well as the so-called delayed allergic reactivities which accompany infection or follow contact with various plant and chemical substances. To this list are added the so-called "collagen" diseases: periarteritis nodosa, disseminated lupus erythematosus, rheumatic fever, rheumatoid arthritis and dermatomyositis; glomerulonephritis, demyelinating encephalomyelitis, and sympathetic ophthalmia; the disorders in which two individuals are concerned, including tissue grafting and transplantation, transfusion reactions, erythroblastosis fetalis and possibly reactions occasioned by platelet and leukocyte group factors; and finally those hematologic disorders, including anemia, thrombocytopenic purpura and agranulocytosis, in which a transfer of cellular or tissue elements between two individuals is not involved.