Different sensitivity of complement to Salmonella typhimurium accounts for the difference in natural resistance to murine typhoid between A/J and C57BL/6 mice

Absent bactericidal activity of mouse serum against invasive African nontyphoidal Salmonella results from impaired complement function but not a lack of antibody

Nontyphoidal strains of Salmonella are a major cause of fatal bacteremia in Africa. Developing a vaccine requires an improved understanding of the relevant mechanisms of protective immunity, and the mouse model of Salmonella infection is useful for studying immunity to Salmonella in vivo. It is important to appreciate the similarities and differences between immunity to Salmonella in mice and men. Ab is important for protection against nontyphoidal Salmonella in both species, and we have previously found an important role for Ab in cell-free complement-mediated bactericidal activity against Salmonella in Africans. It is unclear whether this modality of immunity is relevant in the mouse model. C57BL/6, BALB/c, and C3H mice immunized with heat-killed Salmonella Typhimurium strains D23580 (African invasive strain) and SL1344 and live-attenuated strain SL3261 produced a Salmonella-specific Ab response. Sera from these mice deposited reduced levels of C3 on Salmonella compared with human sera and were unable to kill both wild-type and galE(-) rough mutant of D23580, indicating absent cell-free killing via classical and alternative complement pathways. Supplementing immune mouse sera with human complement enabled killing of Salmonella, whereas addition of human anti-Salmonella Ab to immune mouse sera had no effect. These findings indicate that mouse serum cannot effect [corrected] cell-free complement-dependent killing of Salmonella, because of the reduced mouse complement ability to kill these bacteria compared with human complement. This difference in Ab-dependent immunity to Salmonella in mice and men must be considered when applying findings from the mouse model of Salmonella disease and vaccination response to man.

Wallerian degeneration in C57BL/6J and A/J mice: differences in time course of neurofilament and myelin breakdown, macrophage recruitment and iNOS expression

The lower regeneration potential reported for C57BL/6J mice strain after peripheral nerve lesion may result from alterations in crucial events during Wallerian degeneration. We analysed neurofilament and myelin breakdown, macrophage recruitment, NADPH-diaphorase reaction and inducible nitric oxide synthase (iNOS) expression in transected sciatic nerves of C57BL/6J and A/J mice. The neurofilament volume density was lower in C57BL/6J strain mice at 1 and 3 days after lesion, and later equalled the density observed in A/J. C57BL/6J mice presented a high number of cells containing myelin debris, 3 and 5 days after the lesion. In both strains iNOS immunoreactivity was intense in macrophages and less evident in Schwann cells. However, a delay in macrophage recruitment and a lower percentage of iNOS-expressing macrophages on the third day were observed in C57BL/6J mice. NADPH-diaphorase reaction disclosed a similar pattern for both strains until the seventh day. However, at 5 days, cells with slender processes involving ellipsoid segments showed a well-defined cytoplasmic labelling in C57BL/6J whereas in A/J most of these cells exhibited a more granular and disperse labelling. We propose that these differences between A/J and C57BL/6J strains during Wallerian degeneration may be implicated in the lower regeneration potential observed in the latter.

Mapping lipopolysaccharide response loci in mice using recombinant inbred and congenic strains

Lipopolysaccharide (LPS) induces proliferation of splenic B-cells, and this response was found to be significantly lower in A/J than in C57BL/6J (B6) mice. Several strains and substrains mirrored the high and low responses of B6 and A/J. Assessment of 26 AXB/BXA recombinant inbred (RI) mouse strains identified 23 strains with a low (A/J-like), high (B6-like), or intermediate response. The three remaining RI strains exhibited a novel hyperresponsive phenotype significantly different from that of either founder strain. RI analysis identified four suggestive loci contributing to the LPS response, two of which were confirmed by analysis of congenic strains containing the donor genomic segment from a high- or low-responder strain on the opposite background. The combination of A/J and B6 alleles fixed to homozygosity at the four suggestive loci would occur in only 1 of 256 intercross progeny, but occurred several times among the RI strains.

The full expression of the ity phenotype in ityr mice requires C3 activation by Salmonella lipopolysaccharide

Our previous study has shown that the rapid and sufficient activation of complement by Salmonella lipopolysaccharide occurs in genetically resistant (Ityr) A/J mice. To assess whether the level of complement activation by a virulent strain of Salmonella typhimurium regulates the level of murine natural resistance, we compared levels of serum complement activation by S. typhimurium and kinetics of serum-opsonized S. typhimurium grown in macrophages using several strains of resistant (Ityr) and susceptible (Itys) mice. Itys macrophages killed intracellular S. typhimurium to the same extent as did Ityr macrophages when the pathogen was opsonized with Ityr serum. Opsonization of S. typhimurium with Itys serum reduced intracellular killing activity in Ityr macrophages to the same level as seen with Itys macrophages. Incubation of S. typhimurium with 25% Mg2+ EGTA (5 mm MgCl2-3 mm ethylene glycol-bis (beta-aminotheyl either)-N,N,N',N'-tetraacetic acid)-chelated Ityr serum resulted in higher levels of C3 deposition onto the surface of this bacteria, C3b generation and also C3 consumption, compared with that with Mg2+ EGTA-chelated Itys serum. Opsonization of S. typhimurium with A/J serum prior to infection increased early resistance in Itys mice. Infection with a virulent strain of S. typhimurium induced the expression of interleukin-10 (IL-10) mRNA at higher levels in C57BL/6 mice than in A/J mice. However, opsonization of S. typhimurium with A/J serum decreased bacterial growth in the spleen of C57BL/6 mice to the same level as observed for A/J mice in association with decreased expression levels of IL-10 mRNA. Moreover, administration of anti-C3 antibodies reduced the resistance of A/J mice in association with a decrease in serum levels of C3. These results indicate that the high level of complement activation via the alternative pathway in Ityr serum by a virulent strain of S. typhimurium reduces the virulence of this pathogen, which may contribute to the full expression of Ity phenotype in Ityr mice.

Immunomodulatory properties of Nocardia lysozyme digest (NLD) in complement normal and C5-deficient mice

The constantly increasing number of substances with adjuvant activity outpaces the elucidation of their mode of action. This problem is of great importance as the immunomodulatory action of an adjuvant is time- and route-dependent, which implies that administration at a different moment or site may result in a reduced immune response. In the present work the possibility to achieve dual effect (stimulatory or inhibitory) is regarded in the light of the complement system. The object of the study is a preparation obtained by lysozyme digestion of Nocardia opaca cell walls (NLD). According to the results, the administration of NLD to mice (i.p. at a daily dose of 0.5 mg kg-1) during 3 days prior to the antigen resulted in an inhibition of serum antibody level against sheep red blood cells (SRBC) and lipopolysaccharide (LPS). At the same time, the preparation stimulated the antibody response to SRBC if it was applied after the antigen. The ability of NLD to ensure protection against experimental infection with Klebsiella pneumoniae was comparatively studied in complement-normal mice (strain ICR) and in C5-deficient mice (strain DBA/2). Firstly, it was established that complement-deficient mice were more resistant to infection than complement-normal. Secondly, the preparation expressed a protective effect in C5-deficient animals; nevertheless the inoculation was done s.c. or i.v. The departure of the infection depended on the rate of opsonization of K. pneumoniae. Under certain conditions NLD can provoke excessive C3 activation, which might aggravate the course of the infection. The preparation augmented the host response to second challenge with K. pneumoniae of complement-normal and C5-deficient mice.