Tissue Reactions in Immunity: Some Clinical Implications *

Immunology has thus far been of relatively limited help to physicians in interpreting the immunologic rOle of specific tissue reactions that accompany bacterial invasion. The immunologist has been of outstanding help in bringing to light the defensive properties of the fluids with their antibodies, and of the phagocytes. In interpreting the reactions of the fixed tissues against bacterial attack the tendency of late years has been to consider them as allergic, defining allergy as hypersusceptibility-the opposite of immunity. Considering the intimate contact and the chemical interreactivity of the tissues and fluids, it is difficult to conceive how the tissues can be hypersensitive to the same microorganisms against which the fluids are protective. The basis for the allergic interpretation of specific tissue reactions undoubtedly lies in the fact that they are inflammatory in nature. If a rabbit, for example, is injected subcutaneously with some protein solution, such as horse serum, no significant inflammatory response will be noted and in less than twenty-four hours the area of injection will appear normal. If, about two weeks later, the same rabbit is again injected with horse serum, a marked inflammatory response will be noted in the area of injection. Arthus,1 who first observed this response in 1903, assumed that he dealt with a condition of "local anaphylaxis." This assumption seemed reasonable. Animals usually developed tolerance to repeated injections of many substances. But here was a condition where an animal showed no inflammatory response to a first injection and increasingly marked inflammatory responses to repeated injections given at later periods. The animal tissues must have become hypersusceptible to the protein. Thus has the view become widespread that specific tissue reactions are allergic. During the past four years, studies have been directed in this laboratory to the nature of the tissue responses in the immunized state.' Albino rabbits served as the experimental animals. The