Frank J. Dixon

Murine Models of Systemic Lupus Erythematosus

Publisher Summary This chapter reviews the histopathologic, serologic, lymphocytic, virological, hormonal, and genetic characteristics of murine models of systemic lupus erythematosus (SLE). The pathogenetic mechanisms underlying murine SLE are highly complex, apparently well-programmed genetically, but still diverse and their bases not as yet well defined. Significant serologic and cellular experimental data support the statement that the final immunopathologic perturbation in murine (and human) SLE is a B lymphocyte hyperactivity with corresponding enhancement of serum antibodies and autoantibodies, particularly IgG, and consequent formation of pathogenic antigen–antibody ICs. On the basis of the available data, it appears that this B cell hyperactivity is polyclonal but not necessarily panclonal in nature, because not only antibodies against a wide array of autoantigens but also antibodies against incidental antigens, such as haptens, can be detected. The presence of autoantibodies and of their idiotypes in some recombinant lupus x normal murine lines expressing the normal partners V genes, normal mice in which an exogenous or endogenous (Ipr gene) immunostimulator has been introduced, and unmanipulated normal mice indicate that lupus mice are not unique in their structural genetic Ig elements, whose presence determines the development of their autoimmune disease. The cause of B cell hyperactivity in lupus has not yet been fully elucidated. Autonomous B cell maturation does not appear likely, because B cell proliferation and differentiation in lupus mice was found to be dependent on the same number of accessory signals as in normal mice.

The Raji cell radioimmune assay for detecting immune complexes in human sera.

A sensitivie and simple procedure for the detection and quantitation of soluble complement (C)- fixing immune complexes in sera of patients with various disease states has been developed by utilizing C receptors on Raji cells. These cells lack membrane-bound immunoglobulin but have receptors for IgG Fc, C3b, C3d, and possibly with other C proteins. Uptake experiments showed that both aggregated human gamma globulin (AHG) and 7S IgG bound to receptors for IgG Fc; however, AHG reacted with C bound to cells only via receptors for C and this binding was much more efficient than via IgG Fc receptors. AHG was used as an in vitro model of human immune complexes and its uptake by Raji cells was quantitated by 125I-radiolabeled antihuman IgG. The limit of sensitivity of this test was 6 mug AHG/ml serum. The ability of Raji cells to detect AHG in serum depended on the amount of radioactive antibody used and the size of aggregates. The presence of an excess of C somewhat inhibited binding of AHG containing C to Raji cells. The efficient binding of AHG by receptors for C on Raji cells was used for the detection and quantitation of immune complexes in human sera. Raji cells were incubated with sera to be tested and then reacted with excess radiolabeled antihuman IgG; the amount of radioactivity bound to the washed cells was determined and referred to a standard curve of radioactive antibody uptake by cells previously incubated with increasing amounts of AHG in serum. Thereby immune complexes were detected and quantitated in serum hepatitis, systemic lupus erythematosus, vasculitis, subacute sclerosing panencephalitis, dengue hemorrhagic fever, and malignancies.

Etiopathogenesis of Murine SLE1

Autoimmunity has been considered to represent termination of the natural unresponsive state to self {Weigle 1977). It was originally thought that selftolerance is achieved by elimination of self-reactive lymphocyte clones early in ontogeny (Burnet 1959). However, we now know that such self-reactive clones are normally present in the intact immune system {Clagett & Weigle 1974, Cohen & Wekerle 1973, Bankhurst et al. 1973, Bankhurst & Williams 1975, Sawada et al. 1977, Wigzell 1977) and that self-recognition, based on the complementarity of interacting structures on T cells, B cells and macrophages, is the basis for immune responses {Katz 1977). The prevailing current concept is that self-recognition processes, essential to immune and possibly other physiologic systems, are normally controlled or suppressed by one or more mechanisms that counteract deleterious autoreactive consequences. A variety of events, either exogenous or endogenous, could tip the balance of such regulatory supervision, thereby upsetting its normal damping effect so that harmful autoreactivity is the outcome. Sometimes this imbalance is only transient, superceded by reestablishment of the normal damping mechanism and a return to control over the system. At other times, the defect is permanent, leading to a progressive increase in harmful autoreactivity. This sequence seems to account for the chronic autoimmune phenomena seen in some strains of mice and in certain human diseases, most notably systemic lupus erythematosus (SLE), the prototypic autoimmune disease.

The Biology and Detection of Immune Complexes

Publisher Summary This chapter describes the interaction of immune complexes (ICs) with complement and with the cells of the immune system. The effect of immune complexes depends to a great extent on their antigen–antibody ratio so that their influence, either stimulatory or suppressive, is itself modulated by quantitative aspects of the immune response. The development of numerous techniques for the detection and quantitation of immune complexes has stimulated clinically related research and expanded the list of diseases in which immune complexes appear to play an important role. An extension of this diagnostic technology is the ability to isolate immune complexes and, in turn, their antigenic component, thereby making it possible to identify the antigens involved in immune processes of a great many diseases, including those of unknown etiology. In vivo and in vitro experiments have clarified many factors involved in IC formation, removal, and localization as well as the mechanisms of IC-induced inflammatory reactions. An individual can make an immune response to a large number of exogenous and a smaller number of endogenous antigens. Depending upon the availability of antigen, the antibodies so produced form ICs, which for the most part serve the purpose of aiding the host in eliminating potential pathogens.

Experimental glomerulonephritis: immunological events and pathogenetic mechanisms.

Publisher Summary The chapter reviews several forms of experimental nephritis, especially from the point of view of understanding the pathogenic mechanisms in terms of immunological events. The chapter is arranged in three sections. The first section deals with nephritide caused by antikidney antibodies—namely, the heterologous antikidney antibodies of nephrotoxic serum nephritis. The second section deals with circulating antigen–antibody complex induced nephritis. The third section deals with nephritis produced by immunization to kidney in which both of the above mechanisms appear to play a role. It is now possible to account qualitatively and sometimes even quantitatively for the glomerular changes in two forms of experimental nephritis—namely, those due to nephrotoxic serum and to circulating antigen-antibody complexes. A third form induced by immunization with renal antigens is cause of controversy and confusion. In some species such as the sheep true autoantibodies against glomerular capillaries are produced and are pathogenic, whereas in other species such as the rat the damage is due to complexes of antibody and nonglomerular antigen.

[11] Radioiodination of proteins by the use of the chloramine-T method

Publisher Summary This chapter describes the radioiodination of proteins by the use of the chloramine-T method. The incorporation of radioiodine into protein molecules provides increased dimensions to the study of their interactions and subsequent fates. This incorporation involves the covalent linkage of radioiodine in the tyrosyl and to a lesser degree histidine residue of the protein molecule. Information gained through the use of radioiodinated proteins can be used with confidence if it is established that minimal, if any, alteration occurs in the reactivity of the radioiodinated protein versus that observed in its native form. Chloramine-T radioiodination of proteins involves both the oxidation of radioiodide to its reactive state, H 2 OI + , and the oxidation of sulfhydryl groups of the protein molecules. There must be sufficient chloramine-T available to complete both the reactions. Therefore, proteins, with high reducing capacity, may be poorly radioiodinated under the standard conditions. For example, keyhole limpet hemocyanin under standard conditions is minimally radioiodinated. However, by increasing the chloramine-T to 100/μg per milligram of protein, an average 50% incorporation of radioiodine is achieved with no apparent denaturation. Proteins that cannot be radioiodinated successfully with standard conditions should be repeated at increased chloramine-T to the protein ratios.

The Potential Pathogenic Role of Complement in Dengue Hemorrhagic Shock Syndrome

Abstract In Bangkok, Thailand, 49 of 127 patients with dengue hemorrhagic fever experienced shock. The concentration of nine complement proteins measured in serial serum samples decreased during shock with the exception of C9. C3 and C5 were reduced to 20 to 40 per cent of normal in severe cases. Decrease of plasma fibrinogen, appearance of fibrinogen split products and thrombocytopenia indicated occurence of intravascular coagulation. Metabolic studies of C3 and C1q, performed on 24 patients, indicated a markedly enhanced fractional catabolic rate especially during shock. These results support the concept that activation of complement can constitute a major factor in the pathogenesis of dengue hemorrhagic shock. (N Engl J Med 289:996–1000, 1973)

Shwartzman Reaction after Human Renal Homotransplantation

Abstract In three human recipients, five renal homografts were destroyed within a few minutes to hours after their revascularization in the new host. The kidneys, removed one to 54 days later, had cortical necrosis. The major vessels were patent, but the arterioles and glomeruli were the site of fibrin deposition. There was little or no fixation of host immunoglobulins in the homografts. The findings were characteristic of a generalized Shwartzman reaction. Although the cause (or causes) of the Shwartzman reaction in our patients is not known, they may have been conditioned by the bacterial contamination and hemolysis that often attend hemodialysis, by immunosuppression and by the transplantation itself. Some of the patients have preformed lymphocytotoxic antibodies. Thus, certain patients may be predisposed. High-risk patients should be recognized and treated prophylactically with anticoagulants.

Circulating immune complexes in infective endocarditis.

To examine further the role of immune-complex deposition in infective endocarditis, we studied 29 patients with infective endocarditis for presence of complement-containing circulating immune complexes. Ninety-seven per cent (28 of 29) had serum levels of immune complexes greater than 12 mug per milliliter. Mean levels in these patients were significantly higher than in patients with sepsis without endocarditis or in normal controls (P less than 0.05). Circulating immune-complex levels were correlated with longer duration of illness (P less than 0.025), extravalvular manifestations of endocarditis (P less than 0.025) and hypocomplementemia (P less than 0.05). Patients with right-sided endocarditis had significantly higher circulating immune-complex levels than patients with left-sided involvement (P less than 0.025). In general, levels fell to zero with successful antimicrobial or surgical therapy. This drop was concurrent with disappearance of extravalvular signs, blood cultures becoming sterile, and rise in serum complement levels. These findings support the concept that immune complexes may be important in the pathogenesis of infective endocarditis.

Lymphocytic Choriomeningitis: Production of Antibody by "Tolerant" Infected Mice

Newborn mice infected with lymphocytic choriomeningitis virus are not immunologically tolerant to the agent but, rather, appear to make antibody to the virus. This antibody was detectable only in the kidneys, where presumably it had been deposited in the glomeruli in the form of complexes of antibody, virus, and complement.