David W. Knutson

Circulating Immune Complexes: Their Immunochemistry, Detection, and Importance

The size and molecular composition of circulating immune complexes depend on various factors, including the concentrations and valences of antigens and antibodies and the antigen-antibody ratio. The composition and biological properties of circulating immune complexes, in turn, influence their fate in vivo as well as the likelihood of their detection by various assays. Several assays clearly detect circulating immune complexes, but no single assay has yet been shown to be the most sensitive and the most specific for the entire spectrum of circulating immune complexes. Assays correlate poorly with each other, but this may be desirable if we are to determine which circulating immune complexes have diagnostic, prognostic, or pathogenic importance. Circulating immune complexes are found in numerous rheumatologic disorders and infectious diseases. Their presence in the circulation statistically correlates with disease activity; however, the assays currently used have limited value for diagnosing or aiding in therapeutic decisions. Nevertheless, the future holds promise for such uses.

Immunologic Abnormalities in Hemodialysis Patients: Improvement after Pyridoxine Therapy

8 male patients undergoing maintenance hemodialysis were studied to determine the effect of administering supplements of pyridoxine hydrochloride, 50 mg/day for 3-5 weeks, on tests of immune function. In the 3 patients who initially had abnormal nitroblue tetrazolium reduction tests, the values returned to normal with therapy (p less than 0.05). The generation of chemotactic factors from plasma was defective in all evaluated patients and improved after pyridoxine therapy in 4 of 5 patients (p less than 0.01). The lymphocyte subpopulations changed with a rise in the populations of null cells after supplementation with pyridoxine. In addition, lymphocyte transformation in response to mitogens improved in the 3 patients who initially showed low values in these assays. The improvements occurred with pyridoxine therapy even though some patients who responded had no evidence for vitamin B6 deficiency before therapy, as indicated by a normal erythrocyte glumatic-pyruvic transaminase index. We conclude that several parameters of immune function are improved with pyridoxine supplementation. Studies are necessary to establish the minimum daily intake of pyridoxine which will maintain improved values of these tests of immune function in hemodialysis patients.

Poststreptococcal Acute Glomerulonephritis: Fact and Controversy

Poststreptococcal acute glomerulonephritis is prototypic of the immunologic glomerulonephritides. It most commonly follows streptococcal infection of the pharynx or skin. The diagnosis is usually not difficult when a nephritic clinical presentation (with such manifestations as hematuria, edema, and hypertension) is associated with serologic evidence of recent streptococcal infection and a depressed serum complement concentration. Currently, however, the nephritogenic antigen(s) has not been identified and has not been shown to be the same antigen for all nephritogenic streptococci; it may not even be a part of the infecting organism. The development of a vaccine to prevent this illness from occurring is therefore still not possible. Whether poststreptococcal acute glomerulonephritis progresses to chronic renal failure is still uncertain. Painstaking laboratory research together with careful, prospective long-term follow-up studies of patients with poststreptococcal acute glomerulonephritis may provide some of the answers to these critical questions.

Characteristics of soluble immune complexes prepared from oligovalent DNP conjugates and anti-DNP antibodies

The stability of soluble immune complexes was investigated after isolation by gel filtration and sucrose gradient ultracentrifugation. Soluble immune complexes were formed between specific goat anti-dinitrophenol (DNP) antibodies and DNP conjugated to a large (19 S) carrier, namely bovine thyroglobulin. The composition and molecular weight of these complexes were determined by ultracentrifugation on calibrated sucrose density gradients and the use of different isotopic markers for antigen and antibody. A good separation of immune complexes containing one, two, or three antigen molecules per complex was obtained by ultracentrifugation while gel filtration was less effective. Ultracentrifugational analysis of fractions isolated by these two procedures showed that large immune complexes containing more than one antigen were relatively labile, whereas small immune complexes containing one antigen were stable. The stability of large immune complexes was dependent on dilution. Because dilution affects the size and composition of soluble immune complexes, it is important to emphasize that for the investigation of a causal relationship between the biological properties and the size and composition of immune complexes, analysis of the immune complexes should be performed in the same dilutions in which they will be used experimentally.

Isolation of Stable Aggregates of IgG by Zonal Ultracentrifugation in Sucrose Gradients Containing Albumin

Soluble heat aggregates of [125I]IgG (A-IgG) were prepared and separated by gel filtration or by zonal ultracentrifugation, and fractions containing different size aggregates were then analyzed by reultracentrifugation. A-IgG formed single narrow peaks with constant S rates when isolated, stored and analyzed in solution containing 0.5% serum albumin. Thus, stable homogeneous aggregates of IgG of known size can be simply prepared and should prove useful both as a model for immune complexes of specified sizes and as a standard for immune complex assays.

Characterization and measurement of anti-IgG antibodies in human sera by radioimmunoassay (RIA)

A sensitive direct binding radioimmunoassay (RIA) was developed which detected low avidity anti-IgG antibodies in sera negative in the latex fixation test (LFT). IgG class antibodies could be detected and were commonly found along with IgM class antibodies. Additionally, the RIA was more reproducible than the LFT, was easily adapted to measure relative avidities of anti-IgG antibodies, and had other technical advantages over the LFT.

Recovery of the murine mononuclear phagocytic system following chronic exposure to cadmium

Consistent with our previously reported findings, chronic ingestion of cadmium chloride in drinking water by mice caused a decrease in the rate of circulation clearance of 51Cr-labeled sheep red blood cells (E) and IgG-coated E (E-IgG) due to a decrease in the localization of E and E-IgG in the liver. These decreases reached their nadirs after 15 weeks of cadmium ingestion and remained relatively constant for up to one year during continued ingestion of cadmium. Replacement of the drinking water containing cadmium with regular tap water resulted within 8 days in an improvement in the ability of the mice to clear E and E-IgG. Mice also had a decreased ability to develop delayed-type hypersensitivity reactions while being given cadmium; this abnormality also returned toward normal after withdrawal of cadmium. The return of these two responses toward control levels occurred while there was still a large organ burden of cadmium that was not measurably different from that at cessation of cadmium ingestion.