Delayed and deficient establishment of the long-term bone marrow plasma cell pool during early life.

Early life antibody responses are characterized by a rapid decline, such that antigen-specific IgG antibodies decline to baseline levels within months following infant immunization. This generic observation remains unexplained. Here, we have analyzed the induction and organ-localization of antigen-specific IgG antibody-secreting cells (ASC) following immunization of 1-week-old or adult BALB/c mice with tetanus toxoid (TT), a T-dependent antigen. Early life priming induced only slightly lower numbers of TT-specific IgG ASC in the spleen, and these reached adult levels following repeat immunization. In contrast, early life immunization generated much fewer bone marrow plasma cells than in adults, even after boosting. A similar limitation of the natural development of the bone marrow pool of ASC was observed. Transfer experiments with adult or early life spleen ASC indicated limited homing of TT-specific adult ASC to the bone marrow of 4-week-old mice as compared to adult recipients, whereas homing patterns were similar when early life or adult ASC were transferred into adult recipients. These observations suggest that a limited bone marrow B cell homing capacity and, as a result, relatively deficient bone marrow ASC responses, are critical factors which may explain the limited persistence of IgG antibodies to T-dependent antigens in early life.

A second Candida albicans resistance gene (Carg2) regulates tissue damage, but not fungal clearance, in sub-lethal murine systemic infection.

The severity of systemic infection with the yeast Candida albicans has been shown to be under complex genetic control. C57/L mice carry an allele that is associated with an increase in tissue destruction when compared with C57Bl/6 mice; however, the gene affects only the severity of tissue lesions, and does not influence the magnitude of the fungal burden in either kidney or brain. Studies in [C57/LxC57Bl/6]F1 hybrid mice, and [C57/LxC57Bl/6]F1xC57/L backcross mice, demonstrated that the gene behaves as a simple Mendelian co-dominant.

Increased tissue resistance in the nude mouse against Candida albicans without altering strain-dependent differences in susceptibility.

Strain differences in tissue responses to infection with Candida albicans were examined in nude mice having susceptible (CBA/CaH) and resistant (BALB/c) parentage. Homozygous (nu/nu) mice of both strains were more resistant to systemic infection with C. albicans than heterozygous (nul+) littermates as indicated by a reduction in both the severity of tissue damage and colony counts in the brain and kidney. However, the tissue lesions in nu/nu CBA/CaH mice were markedly more severe than those in nu/nu mice with the BALB/c background. This pattern was reflected in the greater fungal burden in the CBA/CaH strain. Analysis of cDNA from infected tissues using a competitive polymerase chain reaction excluded interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), and interleukin 6 (IL-6) as mediators of the enhanced resistance of the nude mice. The results confirm that the different patterns of lesion severity in BALB/c and CBA/CaH mice do not involve T lymphocyte-mediated pathology, and are consistent with the hypothesis that strain-dependent tissue damage is not dependent on the effector function of macrophages or their precursors.

Evidence that two independent host genes influence the severity of tissue damage and susceptibility to acute pyelonephritis in murine systemic candidiasis.

Tissue damage in the kidney and brain after systemic infection with Candida albicans was examined in recombinant inbred strains (AKXL) derived from AKR and C57/L progenitors. Nine of the 15 strains showed mild (C57/L-like) tissue damage. Of the remainder, two strains developed lesions comparable to the AKR parental strain, whereas four exhibited a much more severe pattern of tissue damage. This was characterized by pronounced mycelial growth in the brain, and gross oedema of the kidney, with extensive fungal colonization and marked tissue destruction. The presence of the null allele of the haemolytic complement gene (Hc) may be necessary, but not sufficient, for the expression of the very severe lesions. The results were interpreted as reflecting the actions of two independent genes, which have been designated Carg1 and Carg2 (Candida albicans resistance genes 1 and 2).

Neutrophil depletion increases susceptibility to systemic and vaginal candidiasis in mice, and reveals differences between brain and kidney in mechanisms of host resistance.

Infections caused by the yeast Candida albicans represent an increasing threat to debilitated and immunosuppressed patients, and neutropenia is an important risk factor. Monoclonal antibody depletion of neutrophils in mice was used to study the role of these cells in host resistance. Ablation of neutrophils increased susceptibility to both systemic and vaginal challenge. The fungal burden in the kidney increased threefold on day 1, and 100-fold on day 4, and infection was associated with extensive tissue destruction. However, a striking feature of the disseminated disease in neutrophil-depleted animals was the altered pattern of organ involvement. The brain, which is one of the primary target organs in normal mice, was little affected. There was a threefold increase in the number of organisms recovered from the brains of neutrophil-depleted mice on day 4 after infection, but detectable abscesses were rare. In contrast, the heart, which in normal mice shows only minor lesions, developed severe tissue damage following neutrophil depletion. Mice deficient in C5 demonstrated both qualitative and quantitative increases in the severity of infection after neutrophil depletion when compared with C5-sufficient strains. The results are interpreted as reflecting organ-specific differences in the mechanisms of host resistance.

Early inflammatory responses to Candida albicans infection in inbred and complement-deficient mice.

Inflammatory responses that developed in the footpad during the first 48 h after inoculation of Candida albicans were compared in six genetically defined inbred strains of mice. Tissue responses consisted predominantly of accumulations of polymorphonuclear leucocytes, the magnitude of which was significantly less in mice lacking the fifth component of complement (C5). Despite this, there was no difference between C5-sufficient and C5-deficient mice in the total infectious burden, nor did depletion of complement by treatment with cobra venom factor cause any detectable reduction in the numbers of inflammatory cells in the area of the lesion. Ablation of granulocytes had no significant effect on the fungal burden over the period of the experiment. Immunisation provided some protection against tissue damage, but did not reduce the number of yeasts at the site of infection.

Strain-dependent differences in host response to Candida albicans infection in mice are related to organ susceptibility and infectious load.

After systemic infection with the yeast Candida albicans, inbred mice show substantial differences in mortality, organ colonization, and severity of tissue damage. To examine the relationships between these variables, which are not directly correlated with each other, fungal colonization of the kidneys and brain was enumerated in six inbred strains that exhibit different patterns of tissue damage and mortality. Mice lacking the fifth component of complement (C5) are highly susceptible to lethal challenge, and A/J and DBA/2 mice, both C5 deficient, showed the highest colony counts in the kidneys after challenge with 10(5) blastoconidia. In contrast, colony counts in the brain of all six strains were equivalent at this challenge dose. A/J and DBA/2 mice died after challenge with 3 x 10(5) blastoconidia, but other strains showed an increase in kidney colonization, and strain-dependent differences in clearance from the brain became evident. The data suggest that mortality in A/J and DBA/2 mice is related to an unusual susceptibility of the kidneys to colonization by C. albicans and that there may be tissue-specific differences in host protective mechanisms.

Acute labyrinthitis associated with systemic Candida albicans infection in ageing mice.

The yeast Candida albicans is an important opportunistic pathogen that has been associated with disease of the inner ear. This study describes the histopathology of acute labyrinthitis caused by systemic infection with C. albicans in aging inbred mice. Within four days after infection, yeast and hyphal forms of C.albicans were found in the membranous labyrinth. The utricle and the adjacent parts of the ampullary regions of the semicircular canals were most severely affected, but damage was also seen in the scala media, the scala tympani, the saccule, and the scala vestibuli. In the utricle, the lining epithelium of the membranous labyrinth was disrupted, and the lining cells of the vestibular membrane showed foci in which the membrane was disrupted. The data suggest that age may represent a risk factor for fungal labyrinthitis.

Cytokine mRNA in brain tissue from mice that show strain-dependent differences in the severity of lesions induced by systemic infection with Candida albicans yeast.

BALB/c and CBA/CaH mice show discrete, genetically determined patterns of tissue responses to infection with the yeast Candida albicans. By use of a semiquantitative reverse transcriptase-polymerase chain reaction, interferon (IFN)-gamma, interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha were readily demonstrated in brain tissue on days 1, 3, and 5 after infection and were present in higher concentrations in CBA/CaH than in BALB/c mice. IL-2 and -4 were detected in both strains but at different time points. Both the fungus burden and the severity of the tissue damage become established before mRNA concentrations of the cytokines increase in the lesions, and the rate of clearance of the yeast is similar in both mouse strains. The data indicate that the deterministic model, which correlates Th1 and Th2 cytokines with resistance and susceptibility, respectively, is inadequate to account for the patterns of cytokine production that develop in the infected brain after sublethal challenge.

Rapid destruction of skeletal muscle fibers by mycelial growth forms of Candida albicans.

The process of tissue invasion by the yeast Candida albicans after subcutaneous inoculation into the footpad of mice has been examined by light and electron microscopy. The blastospores germinated within 2 hr after injection. Hyphal and, to a lesser extent, pseudohyphal elements were observed penetrating into the adjacent striated muscle fibers and the endothelial cells of capillaries and destroying the collagen bundles of the interstitium. Electron microscopy showed evidence of structural tissue degradation associated with the mycelial elements, particularly at the apical tip. This was presumably due to fungal enzymatic activity. By 3 hr after infection, polymorphonuclear leucocytes had engulfed both the extracellular and intracellular mycelia, and often there was structural evidence of mycelial degradation. The results provide morphological evidence that initial tissue damage following subcutaneous infection is caused by the mycelial growth form.