The occurrence of antigenic determinants common to flagella of different salmonella strains

Immunology and immunity studied with viruses

Immunity to viruses is used to define important biological parameters of immunology. Specificity, tolerance and T and B cell memory were analysed with murine model infections. The key parameters of antigen kinetics, localization and patterns of T and B cell response induction in maintaining memory and in causing deletion of reactive lymphocytes were compared for self and for viral foreign antigens. Evidence is reviewed that suggests that B cells essentially recognize antigen patterns, whereas T cells react against antigens newly brought into lymphoid tissues; antigens outside lymphoid tissues are ignored, and antigens always present in, or spreading too fast throughout, lymphoid tissues exhaust and delete T cell responses. Finally, effector mechanisms of antiviral immunity are summarized, as they vary with different viruses. On this basis immunological T and B cell memory against viruses is reviewed. Memory studies suggest that increased precursor frequencies of B and T cells appear to remain in the host independent of antigen persistence. However, in order to protect against cytopathic viruses, memory B cells have to produce antibody to maintain protective elevated levels of antibody: B cell differentiation into plasma cells is driven by persisting antigen. Similarly, to protect against infection with a non-cytopathic virus, cytotoxic T cells have to recirculate through peripheral organs. Activation and capacity to emigrate into solid tissues as well as cytolytic effector function are also dependent upon, and driven by, persisting antigen. Because no convincing evidence is yet available of the existence of identifiable B or T cells with specialized memory characteristics, the phenotype of protective immunological memory correlates best with antigen-driven activation of low frequency effector T cells and plasma cells.

Comparative analysis of flagellin sequences from Escherichia coli strains possessing serologically distinct flagellar filaments with a shared complex surface pattern

Escherichia coli morphotype E flagellar filaments have a characteristic surface pattern of short-pitch loops when examined by electron microscopy. Seven of the 50 known E. coli H (flagellar antigen) serotypes (H1, H7, H12, H23, H45, H49, and H51) produce morphotype E filaments. Polymerase chain reaction was used to amplify flagellin structural (fliC) genes from E. coli strains producing morphotype E flagellar filaments and from strains with flagellar filaments representing other morphotypes. A single DNA fragment was obtained from each strain, and the size of the amplified DNA correlated with the molecular mass of the corresponding flagellin protein. This finding and hybridization data suggest that these bacteria are monophasic. fliC genes from three E. coli serotypes (H1, H7, and H12) possessing morphotype E flagellar filaments were sequenced in order to assess the contribution of conserved flagellin primary sequence to the characteristic filament architecture. The H1 and H12 fliC sequences were identical in length (1,788 bp), while the H7 fliC sequence was shorter (1,755 bp). The deduced molecular masses of the FliC proteins were 60,857 Da (H1), 59,722 Da (H7), and 60,978 Da (H12). The H1, H7, and H12 flagellins demonstrated 98 to 99% identity over the amino-terminal region (190 amino acid residues) and 89% (H7) to 99% (H1 and H12) identity in the carboxy-terminal region (100 amino acid residues). The complete primary amino acid sequences for H1 and H12 flagellins differed by only 10 amino acids, accounting for previously reported serological cross-reactions. However, the central region of H7 flagellin had only 38% identity with H1 and H12 flagellins. The characteristic morphology of morphotype E flagellar filaments is therefore not dependent on a highly conserved primary sequence within the exposed central region. Comparison of morphotype E E. coli flagellins with those from E. coli K-12, Serratia marcescens, and several Salmonella serovars supported the established concept of highly conserved terminal regions flanking a variable central region.

Sequence invariance of the antigen-coding central region of the phase 1 flagellar filament gene (fliC) among strains of Salmonella typhimurium

Previous studies of the phase 1 flagellar filament protein (flagellin) in strains of five serovars of Salmonella indicated that the central region of the fliC gene encoding the antigenic part of the protein is hypervariable both between and within serovars. To explore the possible use of this variation as a source of information on the phylogenetic relationships of closely related strains, we used the polymerase chain reaction technique to sequence part of the central region of the phase 1 flagellar genes of seven strains of Salmonella typhimurium that were known to differ in chromosomal genotype, as indexed by multilocus enzyme electrophoresis. We found that the nucleotide sequences of the central region were identical in all seven strains and determined that both the previously published sequence of the fliC gene in S. typhimurium LT2 and a report of a marked difference in the amino acid sequence of the phase 1 flagellins of two isolates of this serovar are erroneous. Our finding that the fliC gene is not evolving by sequence drift at an unusually rapid rate is compatible with a model that invokes lateral transfer and recombination of the flagellin genes as a major evolutionary process generating new serovars (antigen combinations) of salmonellae.

Immunological relationships between Salmonella flagellins and between these and flagellins from other species of Enterobacteriaceae

Ten antisera raised in rabbits, against polymeric flagellins from ten different Salmonella serotypes were used to determine the relative cross-activities between salmonella flagellins in monomeric form. The results showed a high degree of cross-reactivity between the antisera (IgG antibodies) and all monomeric flagellins investigated. Consequently, it was possible to detect the ten Salmonella serotypes, after heat depolymerization of flagella using radioimmunometric assay with only one antiserum raised against polymeric flagellin from one serotype. The results also showed that native flagella differed antigenically from repolymerized and monomeric flagellins. This is possibly due to changes in the tertiary structure of sub-units of flagella when depolymerized with acid or heat resulting in unfolding and unmasking of common antigenic determinants. The unfolded and unmasked antigenic determinants were not only common to the Salmonella serotypes investigated, but also to other members of Enterobacteriaceae.

Immunological relationships between Salmonella flagella and their potential application for salmonellae detection by immunoassay

Native flagella of ten Salmonella serotypes were shown to possess serotype-specific antigenic determinants as well as a multiple of common antigenic determinants, which varied in concentration. Each common antigenic determinant was shared by certain, but not all, serotypes. This has been demonstrated from agglutination and radioimmunometric assay (RIMA) results, using ten antisera raised in rabbits against purified polymeric flagellins from ten Salmonella serotypes as immunogens. The minimum detectable populations of salmonellae, as determined by RIMA varied considerably, due to variation in concentrations (and possibly types) of common antigenic determinants. However, the results demonstrated the feasibility of utilizing RIMA for the qualitative detection of salmonellae, using a mixture of only the ten antisera and 125I-labelled protein A as a general tracer. In this way, 77 different salmonellae were detected in less than 8 h after culturing in selective broth. The RIMA developed was specific for salmonellae and showed no cross-reactions with high populations of other members within the family Enterobacteriaceae.

Evidence that carrier-specific B cells play a role in cellular collaboration

Evidence is presented showing that carrier-specific B cells play a significant role in inducing an anti-hapten antibody response to the thymus-dependent antigen, dinitrophenylated monomeric flagellin (DNP-MON), both in vivo and in vitro. Inactivation of carrier-specific B cells by (125I) polymeric flagellin (POL) suicide decreased the anti-DNP IgM response by 40%-50% and reduced the anti-DNP IgG response by 85%-90%. Several lines of evidence established that the suicide procedure eliminated carrier-specific B cells rather than carrier-specific T (helper) cells.