Howard C. Thomas In normal subjects the regulatory apparatus of the immune system permits responses to foreign antigens but suppresses those directed to "self' components. Autoimmune disease occurs as a failure ofthis system either as a result of a primary defect in the regulatory apparatus (primary autoimmunization) or because of a change in the antigenicity of the tissues (secondary autoimmunization). Autoaggressive reactions are characterised by the presence of autoantibodies. When these are directed to membrane displayed antigens (Fig. 1) they are probably of importance in the lysis of hepatocytes. Those directed to cytoplasmic antigens may be useful diagnostically but are of unknown pathogenic significance. When no extrinsic aetiological factor can be identified, the process is assumed to be the result of a failure ofthe regulatory system, allowing the spontaneous expansion of a clone of autoreactive lymphocytes. The defect may be generalised or specific to certain groups of self-antigens and thus the autoimmune disease may be either multi- or unisystemic. The recent development of techniques to enumerate and measure the functional activity of the suppressor lymphocytes which control the effector limbs of the immune system has enabled investigators to test whether the various purported autoimmune diseases do have as their basis a generalised defect in immunoregu lation. Assessment of antigen-specific immunoregulatory function is, however, not yet readily available. liver Membrane I Antigen (LIM) I Liver I HLA, A, B, C, Sensitisation to Specific -;::!IIIL. .

The subject of immune deficiency has become of special importance for two reasons. First, conditions with well defined defects in the immune system could be analyzed as "experiments of nature" in terms of finding out the accurate biological relevance of the defective link in the immune system. Secondly, the recognition of immune deficiency states has become important in order to provide the patients with the treatment necessary to remedy these defects. With regard to immune deficiency states in patients, these have been instrumental as "experiments of nature" in the revelation by Drs. Good and Cooper and their associates of the two-component structure of the immune system, a discovery which can be consi dered as a major breakthrough in the history of immunopathology. Today's research allows us to go far beyond this basic two component structure with the assessment of disorders affecting either cell to cell interactions or regarding subsets of lymphocyte populations. Furthermore, the association of immune deficiency with distinct enzymatic defects of purine metabolism is opening the door to the molecular level of immune deficiency. Dr. Cooper and Dr. Lawton have succeeded in obtaining the collaboration of the leaders in the field of immune deficiency. In view of the importance of their contributions in scientific and clinical terms, we decided to prepare a book version of the two issues of Seminars in Immunopathology devoted to this subject."