No abstract

Abstract. In order to evaluate the basis for changes in plasma concentrations ofthe third component of complement (C3) during inflammation, we injected purified radiolabeled C3 into normal New Zealand White rabbits and into rabbits with turpentine-induced pleurisy. In the normal animals, C3 was distributed between the intravascular compartment (75%) and the extravascular space (25%), with an exchange rate of 1.8±0.1% of the plasma pool per hour. The fractional catabolic rate (FCR) was 2.7±0.3% of the C3 plasma pool per hour, the synthesis rate was 1.0±0.2 mg C3/kg per h, and the plasma concentration was 1.23±0.3 mg C3/ml. Rabbits with turpentine-induced inflammation showed a shift of the volume ofC3 distribution in favor ofthe extravascular compartment. In addition, the rate by which '25I-C3 was cleared from the circulation increased by 29% and was related to the appearance of 20% of the C3-bound circulating radioactivity in the affected pleural cavity at the zenith of inflammation. The FCR, calculated by measuring urinary excretion of radiolabel, increased by only 9% and was probably related to the C3 degradation that was observed in the pleural fluid during the early stages of inflammation. The plasma C3 concentration reached a peak at 230% of the baseline concentration, owing to an increase in the rate of synthesis by as much as 480%. The latter increase could be blocked by cycloheximide, an inhibitor of protein synthesis. We conclude that the increase of plasma C3 in the acute phase is due to stimulated synthesis, which is partially offset by a rise in FCR and by a shift of protein to the site of inflammation.Dr. Strunk is the recipient of an Allergic Diseases Academic Award (AI-00543).

Immune adherence is the attachment of C-bearing immune complexes via the major activation fragment of the third component of C(C3b) to C3b binding membrane proteins. On primate E, the C3b-R, termed CR1, mediates immune adherence. In nonprimates, immune adherence involves platelets instead of E. However, these functional data have not been corroborated by the identification of the binding protein. In this work, we have identified a C3b/iC3 binding protein of rabbit platelets and characterized it as a single chain structure with a Mr of 150 kDa (nonreducing) or 175 kDa (reducing). This protein binds to rabbit iC3 or C3b but not C3d. This specificity of binding and the ability to rebind to a second column of iC3- or C3b-thiol-Sepharose are comparable to human CR1. Also, a molecule with the identical Mr as well as other structural and binding characteristics is present on rabbit PBMC. No such protein was isolated from rabbit E. Our data strongly suggest that the C3b/iC3 binding protein of rabbit platelets is the homologue of human CR1. If so, this represents an interesting evolutionary switch in the tissue specific expression of the immune adherence R from platelets in the nonprimate to E in the primate.

Five members of an eight-member family fell ill with an acute icteric hepatitis B of the same subtype within eleven months. In all probability the source of the infection was a just over one-year-old fostered child with asymptomatic chronic persisting hepatitis B and signs of massive viraemia (usually high HBs antigen concentration, high virus-specific DNA-polymerase activity and positive HBe antigen test). No relation could be demonstrated between HLA constellation and illness in the family members. Since no specific treatment is available, the only possible prophylactic measure is to isolate the child in the present environment, to avoid further cases of the disease.