Influence of endotoxin-protein in immunoglobulin G isotype responses of mice to Brucella abortus lipopolysaccharide

Abstract

Brucella abortus endotoxin preparations, containing approximately 5 to 6% protein, induce strong immune and adjuvant immunoglobulin G (IgG) responses as compared with Escherichia coli endotoxin preparations, with equivalent amounts of protein, which induce responses in which IgM antibody predominates. Using an enzyme-linked immunoassay with isotype-specific conjugates, we found that antibody of all four subclasses of IgG were evoked during the course of the immune responses of C3H/HeAu mice to B. abortus endotoxin. Secondary responses of endotoxin-hyporesponsive C3H/HeJ mice were similar to those seen in C3H/HeAu mice, although lower levels of antibody were produced during their primary responses. The primary responses of BALB/c athymic mice consisted almost entirely of IgG3, and IgGl appeared following a second injection.The effects of lipopolysaccharide (LPS)-associated protein on the immunogenic properties of B. abortus endotoxin were examined by comparing responses to endotoxin with those to a purified B. abortus LPS containing <1% protein. The endotoxin evoked strong primary and secondary responses in which antibody directed to LPS determinants consisted mainly of IgG3 and those to the protein determinants were largely IgGl antibody. Primary and secondary responses to purified LPS consisted mainly of IgG3 antibody. The potential mechanism of the contribution of protein to the immunogenic properties of the endotoxin as well as possible immune mechanisms involved in these responses are discussed. 728 on August 3, 2020 by guest

An evolutionary strategy for a stealthy intracellular Brucella pathogen

“…This observation suggests that IFN‐γ influences the IgG isotope synthesis in mice by both Th1‐dependent and ‐independent events. This is also suggested by the IgG3, IgG2a, IgG2b, IgG1 isotype profile generated against purified Br‐ LPS in both euthymic and athymic mice (124).…”

“…There is a higher precursor frequency of IFN‐γ‐producing CD4 + T cells and a lower precursor frequency of IL‐4‐producing CD4 + T cells among these clonogenic cells from B. abortus‐ infected mice than in mice immunized with killed Brucella soluble antigens (119), indicating the preponderance of Th1 response. In addition, during the chronic phase, IL‐10, GM‐CSF, and IL‐4 are barely secreted by spleen cells of Brucella ‐infected mice challenged ex vivo with Brucella antigens (118, 121, 124, 126). This is relevant, because killed Brucella is able to stimulate a significant Th2 and T‐independent responses and no DTH, in clear contrast to the prominent Th1 response induced by the live bacteria (12, 119).…”

Variation of Brucella abortus 2308 infection in BALB/c mice induced by prior vaccination with salt-extractable periplasmic proteins from Brucella abortus 19

“…We suggest that larger doses of antigen perturbed the host normal cellular responses and thereby suppressed the overall host immune system (21,22,29,40). Also, a larger dose of the specific antigen could neutralize or mask a specific effect such as IgG production (an increase in immunoglobulin subclass G3 that is associated with enhanced protection), as seen with LPS vaccines (15,24,30,32,34), while stimulating cellular immunity that was primarily responsible for the reduced numbers of CFU (1,8,9).…”

Immunochemical identification of Brucella abortus lipopolysaccharide epitopes

“…Although simple, these observations are remarkable. With a few exceptions (22,23,33), works involving diagnosis, passive protection, or immune responses against Brucella antibodies to LPS determinants different from those present in O-polysaccharide have been disregarded (5,8,12,20,29,38,39). For instance, LPS antigens containing strongly bound proteins considerably influence the interpretation of serological immunoassays due to the presence of different immunoglobulins directed against protein epitopes (22,33).…”

“…With a few exceptions (22,23,33), works involving diagnosis, passive protection, or immune responses against Brucella antibodies to LPS determinants different from those present in O-polysaccharide have been disregarded (5,8,12,20,29,38,39). For instance, LPS antigens containing strongly bound proteins considerably influence the interpretation of serological immunoassays due to the presence of different immunoglobulins directed against protein epitopes (22,33). This is relevant in light of extensively used EIAs for the diagnosis of bovine brucellosis (19) performed with smooth-type LPS antigens containing variable quantities of LPS-associated proteins and rough-type LPS, as determined by one of us (E.M.).…”