BRUCELLA-MELITENSIS CELL-ENVELOPE PROTEIN AND LIPOPOLYSACCHARIDE EPITOPES INVOLVED IN HUMORAL IMMUNE-RESPONSES OF NATURALLY AND EXPERIMENTALLY INFECTED SHEEP

Cell envelope fraction (CEF) of Brucella melitensis B115 was used to i nvestigate antibody responses of B. melitensis naturally and strain H3 8 experimentally infected sheep by immunoblotting, indirect enzyme-lin ked immunosorbent assay (ELISA) (I-ELISA), and competitive ELISA (C-EL ISA) with monoclonal antibodies (MAbs). MAbs used were directed to out er membrane proteins with molecular masses of 10, 16.5, 19, 25 to 27, 31 to 34, 36 to 38, and 89 kDa; to the heat shock protein DnaK, to O-p olysaccharide (O-PS) common (C) and M epitopes; and to rough lipopolys accharide (R-LPS) epitopes. In immunoblotting, all infected sheep sera tested recognized a large number of protein bands, including the abov e-cited proteins and other proteins for which MAbs have not been defin ed. The antibody response pattern was different from one animal to ano ther, even within the experimentally infected sheep which were infecte d under the same experimental conditions. A number of protein bands me re recognized by the sheep sera prior to experimental infection and by other uninfected sheep sera. The antibody reactivity to these antigen s and others might explain the nonspecific antibody reactivity of sera in I-ELLSA with CEF. C-ELISA confirmed also the individual variabilit y of the antibody responses of infected sheep to protein antigens. Ant ibody responses to O-PS C and M epitopes were detected in all experime ntally infected sheep and in half of the naturally infected sheep, but these responses were also heterogeneous in relation to their intensit ies. Antibody responses to R-LPS epitopes detected by use of C-ELISA w ith the anti-R-LPS MAbs were low or negative in most of the infected a nimals. Despite antibody response heterogeneity for CEF antigens, immu noblot and C-ELISA results indicated that, among the CEF antigens, the O-PS epitopes (C and M epitopes) and epitopes of the major 25- to 27- and 31- to 34-kDa outer membrane proteins seem to be the most promisi ng for detecting B. melitensis infection in sheep.