Resistance and susceptibility to infection in inbred murine strains. I. Variations in the response to thymic hormones in mice infected with Candida albicans

Genetic analysis of resistance to infections in mice: A/J meets C57BL/6J

Susceptibility to infectious diseases has long been known to have a genetic component in human populations. This genetic effect is often complex and difficult to study as it is further modified by environmental factors including the disease-causing pathogen itself. The laboratory mouse has proved a useful alternative to implement a genetic approach to study host defenses against infections. Our laboratory has used genetic analysis and positional cloning to characterize single and multi-gene effects regulating inter-strain differences in the susceptibility of A/J and C57BL/6J mice to infection with several bacterial and parasitic pathogens. This has led to the identification of several proteins including Nrampl (Slc11a1), Birc1e, Icsbp, C5a, and others that play critical roles in the antimicrobial defenses of macrophages against intracellular pathogens. The use of AcB/BcA recombinant congenic strains has further facilitated the characterization of single gene effects in complex traits such as susceptibility to malaria. The genetic identification of erythrocyte pyruvate kinase (Pklr) and myeloid pantetheinase enzymes (Vnn1/3) as key regulators of blood-stage parasitemia has suggested that cellular redox potential may be a key biochemical determinant of Plasmodium parasite replication. Expanding these types of studies to additional inbred strains and to emerging stocks of mutagenized mice will undoubtedly continue to unravel the molecular basis of host defense against infections.

Genetic analysis of innate immunity in resistance to Candida albicans

Systemic candidiasis is a significant cause of nosocomial infections and the mechanisms of defense against Candida albicans in humans remain poorly understood. Studies in animal models have demonstrated the importance of innate immunity in controlling the response to infection. Although Th1 cytokines have been shown to direct the overall outcome of infection, the precise role of the Th1/Th2 response and, more generally, the adaptive immune response as a whole, in systemic candidiasis, appears to apply mainly to the development of resistance to reinfection. A genetic approach to the identification of host factors regulating pathogenesis and susceptibility to C. albicans infection has been used in humans and in mouse models of infection. Mouse mutants bearing experimentally induced mutations in specific genes have provided a systematic tool for directly assessing the role of individual proteins in C. albicans susceptibility. Inbred mouse strains have been valuable in showcasing the spectrum of naturally occurring variations in initial susceptibility to infection, and type of disease developed. Crosses between resistant and susceptible strains have led to the detection of additional gene effects affecting innate immunity. Of particular interest is the major effect of a naturally occurring loss-of-function mutation in the C5 complement component that has become fixed in many inbred strains. These and other studies have shown that both a functional complement pathway and robust inflammatory response are critical for resistance to C. albicans.

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).

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.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.

Adherence of Candida albicans to tissues from mice with genetic immunodeficiencies

Ex vivo adherence comparisons were made between immunocompetent and immunocompromised mouse tissues, and the roles of serum immunoglobulin and macrophages in the adherence of Candida albicans were investigated. Spleen, lymph node, and kidney tissues were harvested from congenitally immunodeficient mice, including AKR/scid, C.B-17, C3Hscid, and N:NIH nu/bg/xid mice, and their normal counterparts into which the defects were bred (AKR/J, C3H/HeSnJ, and BALB/c-ByJ). Tissues were compared for the ability to bind C. albicans 219 in an ex vivo assay. In general, immunodeficiencies significantly decreased binding of C. albicans to spleen but not to lymph node or kidney tissue compared with immunocompetent mice. In C3Hscid and AKRscid mice, spleen tissues from "nonleaky" mice bound significantly fewer yeast cells (P = 0.0005 and 0.0009, respectively) than did those from C3H/HeSnJ or AKR/J mice. Numbers of adherent yeast cells were similar in "leaky" AKRscid and AKR/J mice. Yeast adherence to spleen tissue from N:NIH nu/bg/xid mice correlated with mouse age (P = 0.01). Measurements of total serum immunoglobulin indicated that the scid defect was most complete in C3Hscid mice and that yeast adherence in spleen tissue correlated with immunoglobulin titers. Results of adherence assays and macrophage-specific immunostains suggested that factors determining adherence differ among reticuloendothelial organs.

Prediction of "hot spots" in interleukin-2 based on informational spectrum characteristics of growth-regulating factors. Comparison with experimental data

The Resonant Recognition Model (RRM) is a theoretical method for analysis of protein and nucleotide sequences, based on the Fourier transform of the numerical representation of sequences. The amplitude spectrum of this transform is designated Informational Spectrum (IS). There are certain common frequencies in IS of growth-regulating factors. These characteristic frequencies may correlate with their roles in cell proliferation and metabolism, and in antitumor activity. IS of IL-2 has prominent characteristics in the main frequency domain of growth factors, frequency domain of antitumor factors, and frequency domain characteristic for IL-2-alpha receptor. By means of the inverse method for these 3 domains, the amino acids in the sequence of human IL-2 that may be relevant to its biological function, the so-called "hot spots", were predicted. The most probable hot spots, obtained in this way, are in the potential binding site of IL-2 to its receptor, which agrees with experimental data.

Characterization of the immunoregulatory properties of thymosin alpha 1 on interleukin-2 production and interleukin-2 receptor expression in normal human lymphocytes

Thymosin alpha 1 (T alpha 1) and thymosin fraction 5 (TF5) have been shown to induce lymphocyte maturation and differentiation as well as to modulate mature immune responses to antigens and mitogens. The present study focused on the characterization of the mechanisms involved in T alpha 1 and TF5 enhancement of phytohemagglutinin (PHA)-induced interleukin-2 (IL-2) secretion and interleukin-2 receptor (IL-2R) expression in human mononuclear cells. We provide evidence that TF5 and T alpha 1 modulate an early event(s) during lymphocyte activation by mitogens. A short preincubation period (30 min) of non-adherent cells with thymosins, followed by extensive washing and subsequent exposure to PHA, was sufficient to enhance the production of IL-2 and the expression of IL-2R induced by the mitogen. Furthermore, the concomitant addition of PHA and thymosin during the preincubation period is not necessary for the enhancing effects to occur. We have also studied the role of macrophages on thymosin modulation of these responses. Results presented here indicate that macrophages are not essential for the interaction of thymosins with T-cells. However, macrophages are an absolute requirement during the exposure to the mitogen after preincubation with thymosins for the manifestation of TF5- and T alpha 1-mediated enhancing effects on IL-2 production and IL-2R expression. Human recombinant interleukin-1 beta (rIL-1 beta) was able to replace this macrophage requirement, indicating that production of IL-1 by these cells is a critical event in thymosin modulation of the IL-2 system. Two-color flow cytometric analysis and experiments involving the use of highly purified helper/inducer (Th, CD4+) and cytotoxic/suppressor (Tc, CD8+) T-cell populations indicated that both, Th and Tc cell populations are targets of thymosin activity. These studies provide additional evidence that thymosins play an important role in the modulation of the normal immune response and begin to define the mechanisms underlying T alpha 1 immunoregulatory properties.

The amino acid sequence of bovine thymus prothymosin alpha

Prothymosin alpha has been purified from calf thymus and its amino acid sequence determined. It contains 109 amino acid residues and closely resembles human prothymosin alpha, with only two substitutions, glutamic acid for aspartic acid at position 31 and alanine for serine at position 83. This is in contrast to six differences between rat and bovine prothymosins, including four substitutions and two deletions. The structural similarity of the bovine and human polypeptides makes the former a good candidate for studies on the evaluation of the biological activities of prothymosin alpha in human systems.

The effect of dietary zinc and prothymosin alpha on cellular immune responses of RF/J mice

Mice of the RF/J strain on a normal diet are defective in some aspects of cellular immunity, as evidenced by their susceptibility to infection with Candida albicans, their failure to release detectable quantities of circulating migration inhibitory factor (MIF) in vivo, and the presence of a low rate of phagocytosis and killing by peritoneal macrophages. When the mice were fed a high-zinc diet (300 ppm) for 4 weeks and then treated daily with 160 ng prothymosin alpha, an increase occurred in resistance to infection with C. albicans, in the capacity to release MIF in vivo into the circulation and in the capacity of peritoneal macrophages to engulf (phagocytose) and kill cells of C. krusei. In addition, the number of spleen lymphocytes producing antibody to a T-dependent antigen was significantly increased in the mice fed a high-zinc diet and inoculated daily with prothymosin alpha.

The human prothymosin alpha gene is polymorphic and induced upon growth stimulation: evidence using a cloned cDNA

Clones for human prothymosin alpha have been identified in cDNA libraries from staphylococcal enterotoxin A-stimulated normal human lymphocytes and from simian virus 40-transformed fibroblasts. The 1198-base-pair fibroblast clone has been sequenced. The encoded protein is highly acidic (54 residues out of 111) and shares greater than 90% sequence homology with rat prothymosin alpha. The peptide "hormone" thymosin alpha 1 appears at positions 2-29 of the prothymosin alpha amino acid sequence. There is no N-terminal signal peptide. Examination of mouse and human tissues revealed the presence of prothymosin alpha mRNA in kidney, liver, spleen, normal lymphocytes (predominantly T cells), human T-cell leukemia virus-infected T cells, and myeloma cells (B-cell lineage). Prothymosin alpha mRNA is inducible; upon mitogen stimulation it increased greater than 15-fold above the level found in resting lymphocytes. Similarly, serum-deprived NIH 3T3 cells responded to serum restitution with an increase in prothymosin alpha mRNA. Characterization of human genomic DNA by Southern blot analysis disclosed a complicated pattern consistent with genetic polymorphism. These data suggest that prothymosin alpha plays an intracellular role tied to cell proliferation. There is no evidence that it serves as a precursor for secreted thymic peptides. However, given the complexity at the genomic level, multiple functions, including a putative secretory capability, cannot be excluded.

Human prothymosin alpha: amino acid sequence and immunologic properties

Prothymosin alpha has been purified from human thymus and its amino acid sequence determined, except for a 15 amino acid segment including 10 glutamyl residues near the middle of the molecule. Like prothymosin alpha from rat thymus [A. A. Haritos, R. Blacher, S. Stein, J. Caldarella, and B. L. Horecker (1985) Proc. Natl. Acad. Sci. USA 82, 343-346], human prothymosin contains the thymosin alpha 1 sequence at its NH2-terminus. It contains a total of 109-110 residues compared to 111-112 for rat prothymosin alpha, with deletions corresponding to positions Gln39 and Lys108 of the rat polypeptide. Human prothymosin alpha also differs from rat prothymosin alpha at positions corresponding to residues 87, 92, and 102 of the latter, with substitutions of alanine for proline, alanine for valine, and aspartic acid for glutamic acid, respectively. Human prothymosin is significantly less active than rat prothymosin in protecting mice against infection with Candida albicans and in stimulating release in vivo of migration inhibitory factor. Thus, the differences in amino acid sequences, present mainly the COOH-terminal half of the polypeptides, may determine species specificity in biological properties.

Delayed-type hypersensitivity and immunity to Salmonella typhimurium

Studies were carried out to correlate immunity and expression of delayed-type hypersensitivity (DTH) in mice of the C3H lineage immunized with an avirulent strain of Salmonella typhimurium (strain SL3235). This strain belongs to a class of aroA- organisms which are being considered as vaccine strains for humans and veterinary use. In a systematic study, the relationship between the mouse strain and the immunizing dose of strain SL3235 on the development of protective immunity and DTH was examined. It was found that in hypersusceptible C3H/HeJ and C3HeB/FeJ mice, several doses of strain SL3235 afforded protection against intravenous challenge doses as high as 1,300 50% lethal doses. Despite these significant levels of immunity to challenge, mice of these two strains never mounted significant DTH responses following immunization with the doses of strain SL3235 tested, which spanned 3 orders of magnitude. Nonresponsiveness was not due to antigen overload, as all of the mouse strains were comparably colonized with strain SL3235 at the time of DTH elicitation. Further, it was found that the ability of responsive C3H/HeNCrlBR mice to display DTH was dependent on the immunizing dose of strain SL3235 and that a dosage could be found that resulted in increased resistance to challenge in these mice without a concomitant display of DTH. Thus, while both induction of protective immunity and DTH were vaccine dosage dependent in the responsive mouse strain (C3H/HeNCrlBR), DTH was a less sensitive measure of protective immunity than survival. Vaccine dosages ranging over three orders of magnitude failed to yield positive footpads to the Salmonella elicitin in the nonresponsive mice. The data suggest that caution should be observed in interpreting Salmonella DTH tests that are used as screens of immune status to typhoid fever in humans, as the extent of discordance between immunity and DTH in humans is unknown.

Thymic hormones in radiation-induced immunodeficiency. I. Induction of mature interleukin 1 responsive cell in the thymus by thymosin fraction 5

The restorative effect of thymosin fraction 5 (TF5) on the thymus of gamma-irradiated mice was examined. Four different mouse strains were used in this study since earlier work determined that the degree of response to TF5 is strain dependent. The responsiveness to comitogenic effect of interleukin 1 (IL-1) was used to measure the rate of recovery of immunocompetent cells in the thymus, since only more mature PNA-, Lyt-1+-2- medullary cells respond to this monokine. Contrary to several earlier reports that radioresistant cells repopulating the thymus within the first 10 days after irradiation are mature, corticosteroid resistant, immunocompetent cells, the thymic cells from irradiated mice in all strains used had greatly reduced responses to IL-1. Daily intraperitoneal injections of TF5 increased significantly the responses of thymic cells to IL-1 in 10- to 13-weeks-old C57Bl/KsJ, C57Bl/6, C3H/HeJ, and DBA/1 mice. Older mice, 5 months or more in age, of DBA/1 strain did not respond to treatment with TF5. However, C3H/HeJ mice of the same age were highly responsive. In conclusion, (1) cells repopulating the thymus within 12 days after irradiation contain lower than normal fraction of mature IL-1 responsive cells, (2) thymic hormones increase the rate of recovery of immunocompetent cells in the thymus, and (3) the effect of thymic hormones is strain and age dependent.

Dissociation between cell-mediated immunity and acquired resistance in systemic murine candidiasis

Mice immunized with 10(7) heat-killed (HK) Candida albicans injected subcutaneously with or without BCG, used as an immunoadjuvant, were able to develop strong significant delayed-type hypersensitivity (DTH) against C. albicans but without any increase in specific resistance, as measured by median survival time and enumeration of yeasts inside target organ such as lungs, liver, spleen and kidneys after an intravenous (i. v.) challenge of 1 X 10(6) live C. albicans. Concomitant activation of the mononuclear phagocytic system, measured in vivo by increased resistance to L. monocytogenes, was shown to be induced in immune mice challenged i. v. with 1 X 10(6) HK C. albicans. These results are in favour of a clear distinction between DTH and acquired resistance to systemic candidiasis, even in the presence of specific activation of macrophages.

Strain variation of lymphokine production and specific antibody secretion in mice infected with Mycobacterium lepraemurium

Mice from strains showing either phenotypical expression of Bcg gene (C57BL/6, BALB/c, DBA/1, and (C57BL/6 X DBA/2)/F1, CBA, A/J, DBA/2) were infected intravenously with 10(7) Mycobacterium lepraemurium (MLM). The number of acid-fast bacilli (AFB) within the spleens, the ability of spleen cells to produce in vitro interleukin 1 and 2, and the serum levels of specific anti-MLM antibodies were assessed 3 months later. The number of AFB recovered from the spleens of various strains followed the strain distribution of genetically controlled innate resistance established for Mycobacterium bovis infection. A decrease of interleukin 2 production by spleen cells could be detected in C57BL/6, DBA/1, DBA/2 and (C57BL/6 X DBA/2)F1 mice only. The level of anti-MLM antibodies was found to be higher in C57BL/6, BALB/c and A/J mice than in the other strains tested. Thus no evidence appeared of a direct influence of the Bcg gene on lymphokine production and antibody secretion.

Parathymosin alpha: a peptide from rat tissues with structural homology to prothymosin alpha

A peptide, parathymosin alpha, containing approximately equal to 105 amino acid residues, has been isolated from rat thymus, and the sequence of the first 30 residues at the NH2 terminus has been determined. In this region, it shows 43% structural identity with thymosin alpha 1 and prothymosin alpha. The common sequences do not include residues 2-9, which accounts for the poor reactivity of parathymosin alpha with an antibody directed against this epitope in thymosin alpha 1. Parathymosin alpha appears to modulate the action of prothymosin alpha in protecting sensitive strains of mice against opportunistic infection with Candida albicans.

Primary structure of rat thymus prothymosin alpha

The primary structure of prothymosin alpha from rat thymus, containing 113 amino acid residues, is reported as follows: (formula; see text) The sequence of the first 28 amino acids at the NH2 terminus is identical to that of calf thymosin alpha 1. The dicarboxylic amino acids, which account for nearly half of the total residues in prothymosin alpha, are largely clustered in the central portion of the polypeptide chain. The polypeptide contains no aromatic or sulfur-containing amino acids. A computer analysis of the three-dimensional structure based on the primary sequence suggests that the molecule is composed of at least five alpha-helical regions interrupted by one short extended chain and three short random coils.

Resistance and susceptibility to infection in inbred murine strains. IV. Effects of dietary zinc

Mice of several inbred strains have been fed diets containing either large amounts of zinc (300 ppm Zn), small amounts of zinc (5 ppm Zn), or routine laboratory mouse chow. When the mice are fed on a high-zinc diet, murine strains, such as C3H/HeJ, AKR/J, and CBA/CaJ, which are normally susceptible to infection with Candida albicans and which normally release low titers of migration-inhibition factor (MIF) in vivo into the circulation, become more resistant to infection with C. albicans and release higher titers of MIF in vivo into the circulation. In addition, their capacity to elicit delayed type hypersensitivity responses may be enhanced. When the mice are maintained on a low-zinc diet, murine strains, such as C57Bl/10SNJ, which are normally resistant to infection with C. albicans and which normally release high titers of MIF in vivo into the circulation on appropriate antigenic challenge, become more susceptible to infection and release lower titers of MIF into the circulation. Under these conditions of low-zinc concentrations in the diet, their capacity to elicit delayed type hypersensitivity may be reduced. Thus, the concentration of zinc in the diet may have a pronounced effect on some in vivo parameters of cell-mediated immunity.

Thymosin alpha 11: a peptide related to thymosin alpha 1 isolated from calf thymosin fraction 5

Two peptides related to thymosin alpha 1 have been isolated from preparations of calf thymosin fraction 5. One, lacking four amino acid residues at the COOH terminus, is designated des-(25-28)-thymosin alpha 1. The other, named thymosin alpha 11, contains seven additional amino acid residues at the COOH terminus. The sequence of this peptide is: AcSer-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu- Lys-Glu-Lys- Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-Gly-Arg-Glu-Ala-Pro-Ala-AsnOH. Thymosin alpha 11, in doses of less than 300 ng per mouse, protects susceptible inbred murine strains against opportunistic infections with Candida albicans. It is approximately equal to 30 times as potent as thymosin fraction 5 and approximately equal in potency to thymosin alpha 1.

Resistance and susceptibility to infection in inbred murine strains. II. Variations in the effect of treatment with thymosin fraction 5 on the release of lymphokines in vivo

Of nine inbred murine strains sensitized intravenously with killed lyophilized Candida albicans and challenged 3 weeks later with a C. albicans filtrate, four strains were low responders and five were high responders in the in vivo release of migration inhibitory factor (MIF) and gamma interferon (IFN-gamma). An identical distribution of high- and low-responder strains occurred in response to sensitization with Mycobacterium bovis BCG and subsequent challenge with old tuberculin. Treatment of the murine strains with thymosin fraction 5 prior to sensitization and challenge had different effects: (a) the high-responder strains had a decrease in their release in vivo of the two lymphokines; (b) three of five of the low-responder strains had a striking increase in the in vivo release of MIF and IFN-gamma; and (c) one low-responder strain did not have its response altered. A parallelism existed between the capacity of a murine strain to release the two lymphokines in vivo on stimulation with C. albicans antigens and the capacity of that strain to resist intravenous infection with living C. albicans.