Characteristics of So-Called Natural Antibodies in Various Normal Sera against Culture Forms of Leishmania

Abstract

Sera from guinea pigs, rats, mice, hamsters, gerbils, and rabbits were tested against promastigotes (leptomonads) of Leishmania brasiliensis, L. donovani, and L. tropica. All sera were able to lyse and agglutinate, to varying degrees, these forms of the 3 species of Leishmania. However, lysis and agglutination were not completely independent. When guinea pig, rat, gerbil, or rabbit serum was inactivated (56 C for 30 min) agglutination of promastigotes was unaffected, but in some cases lysis was reduced or eliminated. The lysis was completely abolished by heating to 65 C for 30 min. Rabbit serum treated with 2-mercaptoethanol was unable to lyse or agglutinate promastigotes, but that treated with zymosan or EDTA (to remove complement) eliminated the lytic effect only. When normal rabbit serum was fractionated on Sephadex G 200, agglutination could be identified with one fraction (IgM) which, with the addition of complement, was also lytic. When normal rabbit serum was absorbed with the culture forms of L. brasiliensis, L. donovani, L. tropica, Trypanosoma cruzi, T. gambiense, T. rhodesiense, or Crithidia sp., the lytic and agglutinogenic activities of the rabbit sera against the 3 species of promastigotes were reduced or eliminated. With respect to lysis, it is possible that other than immunological factors present in the serum could also produce similar effect. Following Laveran's (1902) early description of lysis of Trypanosoma brucei in normal human serum, additional studies extended this observation to other protozoan parasites. Yorke et al. (1930) demonstrated lysis of T. rhodesiense, T. equiperdum, and T. congolense in normal human sera, and Weinman (1953) found that trypanosomes of African sleeping sickness were similarly affected by human and rabbit sera. Muniz and Borriello (1945), Rubio (1956), and Warren (1958) reported both agglutination and lysis of T. cruzi in sera from man, other mammals, and birds. Similar observations were reported by Terry (1957) with T. vivax in sera from normal cotton rats. Lysis of culture forms of various species of Leishmania by normal sera was demonstrated by Adler (1940), Taub (1956), Lainson and Strangways-Dixon (1963), and Ben Raschid (1967). Immobilization, morphological alterations, agglutination, and lysis were observed after treatment of Trichomonas with diluted or undiluted normal sera (Weld and Kean, 1958; Reisenhofer, 1963; Samuels and Chun-Hoon, 1964). This work is a detailed study of lysis and agReceived for publication 24 February 1970. * Guest Worker. Fellowship holder from the Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina. Award F05-TW-1468-02, U.S.P.H.S. glutination of promastigotes (Hoare and Walace, 1966) of L. brasiliensis, L. donovani, and L. tropica, in sera from several species of laboratory animals, and of factors in the serum of rabbits which are involved in the above phe-