By affinity chromatography with a monoclonal antibody (163B6), obtained in our laboratory, we have isolated a T. cruzi antigen which could be useful for differential diagnosis of Chagas' disease from leishmaniasis. This antigen, a 52-kD protein, reacted with all sera from Chagas' disease patients tested but not with sera from patients with leishmania, in ELISA. The 52-kD antigen is widely distributed in the Trypanosoma genus since the 163B6 monoclonal antibody reacts with T. rangeli and 8 strains and a clone of T. cruzi epimastigotes.
We studied the effects of alkali metal cations on the terminal stages of complement lysis of human and sheep HK erythocytes. Sensitized (EA) were reacted with limited amounts of complement for 1 hr at 37°C in buffer containing 147 mM NaCl (Na buffer), which resulted in 10-40% lysis. The unlysed cells were washed with Na buffer at 0-2°C and incubated for 1 hr at 37°C in buffers containing 147 mM of the various alkali metal cations. Although additional lysis (25 to 65%) occured with K, Rb, or Cs buffer, only minor degrees developed with Na or Li buffer. Intermediate levels occured with 100 mM of the divalent alkali cations. Halogen ions and SCN- (147 mM), Ca++ (0.15 mM), and Mg++ (0.5 mM) did not alter the effect of the alkali metal cations. Lysis occuring in K+, Rb+ or Cs+ proceeded without lag, was temperature dependent with an optimum of 43°C, and had a pH optimum of 6.5. Lysis in K and Na buffers was unaffected by 10-3 to 10-5 M ouabain. Experiments with mixtures of cations indicated that Na+ had a mild inhibitory effect that could be totally overcome by K+, partially by Rb+, and not at all by Cs+. Li+ had a strong inhibitory effect, 6 × 10-5 M causing 50% inhibition in buffers containing 147 mM K+, Rb+, or Cs+.
By using intermediate complexes of EA and purified complement components we demonstrated that K+ enhances the lytic action of C8 on EAC1-7 as well as that of C9 on EAC1-8. It was known that Li+ facilitates lysis when acting on the entire complement reaction. We found that Li+ enhanced the lytic action of C8 on EAC1-7, with a kinetic that differed from that of the K+ effect. In addition, Li+ inhibited the enhancing effect of K+ upon lysis of EAC1-8 by C9. This occured at concentration of Li+ similar to those which inhibited the additional lysis by K+, Rb+, Cs+ of cells that were pretreated in Na buffer with the entire complement sequence. We propose that the major effects of alkali metal cations on complement lysis are due to their interaction with C8 and/or membrane constituents.
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