Induction of autophagy correlates with increased parasite load of Leishmania amazonensis in BALB/c but not C57BL/6 macrophages

We investigated the role of autophagy in infection of macrophages by Leishmania amazonensis. Induction of autophagy by IFN-γ or starvation increased intracellular parasite load and the percentages of infected macrophages from BALB/c but not from C57BL/6 mice. In contrast, starvation did not affect the replication of either Leishmania major or Trypanosoma cruzi in BALB/c macrophages. In BALB/c macrophages, starvation resulted in increased monodansylcadaverine staining and in the appearance of double-membrane and myelin-like vesicles characteristic of autophagosomes. Increased parasite load was associated with a reduction in NO levels and was attenuated by wortmannin, an inhibitor of autophagy. In infected macrophages from BALB/c, but not from C57BL/6 mice, starvation increased the number of lipid bodies and the amounts of PGE₂ produced. Exogenous PGE₂ increased parasite load in macrophages from BALB/c, but not C57BL/6 mice. The cyclooxygenase inhibitor indomethacin prevented the increase of parasite load in starved BALB/c macrophages, and actually induced parasite killing. These results suggest that autophagy regulates the outcome of L. amazonensis infection in macrophages in a host strain specific manner.     

Characterization of single nucleotide polymorphisms for a forward genetics approach using genetic crosses in C57BL/6 and BALB/c substrains of mice

Forward genetics is a powerful approach based on chromosomal mapping of phenotypes and has successfully led to the discovery of many mouse mutations in genes responsible for various phenotypes. Although crossing between genetically remote strains can produce F₂ and backcross mice for chromosomal mapping, the phenotypes are often affected by background effects from the partner strains in genetic crosses. Genetic crosses between substrains might be useful in genetic mapping to avoid genetic background effects. In this study, we investigated single nucleotide polymorphisms (SNPs) available for genetic mapping using substrains of C57BL/6 and BALB/c mice. In C57BL/6 mice, 114 SNP markers were developed and assigned to locations on all chromosomes for full utilization for genetic mapping using genetic crosses between the C57BL/6J and C57BL/6N substrains. Moreover, genetic differences were identified in the 114 SNP markers among the seven C57BL/6 substrains from five production breeders. In addition, 106 SNPs were detected on all chromosomes of BALB/cAJcl and BALB/cByJJcl substrains. These SNPs could be used for genotyping in BALB/cJ, BALB/cAJcl, BALB/cAnNCrlCrlj, and BALB/cCrSlc mice, and they are particularly useful for genetic mapping using crosses between BALB/cByJJcl and other BALB/c substrains. The SNPs characterized in this study can be utilized for genetic mapping to identify the causative mutations of the phenotypes induced by N-ethyl-N-nitrosourea mutagenesis and the SNPs responsible for phenotypic differences between the substrains of C57BL/6 and BALB/c mice.     

Xenotropic virus-related restriction patterns of non-H-2 histocompatibility mutant mice strains

The relationship between alteration in the number of xenotropic virus-related sequences and non-H-2 histocompatibility (H) mutations in mice was investigated. Mutant classifications included gain, loss, and loss-gain mutations. Genomic DNA from a panel of non-H-2 H mutant strains on the C57BL/6 and BALB/c backgrounds was digested with a set of restriction enzymes with varying numbers of sites within endogenous xenotropic-related sequences. The digested DNA was then resolved on agarose gels. Southern blots of digested DNA were hybridized with the pX_env probe specific for the env sequence of xenotropic viral sequences. The number of hybridizing bands varied from 7 to 19, depending on the restriction enzyme and inbred background. Most mutant strains were identical in their restriction patterns to the respective background strains. However, two B6 mutant strains, KH84 and HZ54, differed from C57BL/6 at a single band which appeared to be inherited from BALB/c in the derivation of the two congenic strains. The HZ43 strain lacked a male-specific band shared by both C57BL/6 and BALB/c; this loss was evidently independent of the original mutation which was observed to be autosomal. However, the KH148B and KH84 strains on the C57BL/6 background lacked single B6 bands. Both mutants were classified as gain mutants. An examination of previous reciprocal graft rejection patterns and retrovirus linkage to non-H-2 H loci indicated a strong inverse relationship between a linked retroviral sequence and presentation of a non-H-2 H antigen. This inverse correlation is consistent with reports of gene inactivation following retroviral insertion.     

Teratocarcinoma transplantation rejection loci: AnH-2-linked tumor rejection locus

Embryoid bodies (ascites tumor) from a 129/Sv transplantable teratocarcinoma produce tumors (100%) in syngenic 129/Sv mice but fail to form tumors (3–6%) in BALB/c mice, C3H/He mice and C57BL/6 mice, in spite of the fact that the malignant stem cells of this tumor do not express detectable H-2 antigens. The available evidence indicates that this allogeneic tumor restriction has an immunological basis; 100% of the F₁ hybrid mice between 129/Sv and the three other inbred mouse strains accept the 129/Sv teratocarcinoma. The backcross and F₂ mice segregate the BALB/c, C3H/He and C57BL/6 tumor transplantation rejection loci in a manner that indicates that each of these inbred strains of mice contain one to two major transplantation rejection loci. A linkage analysis in the BALB/c and C3H/He backcross and F₂ generations indicates that these mice have a teratocarcinoma transplantation rejection locus on chromosome 17, about eight to nine recombination units from theH- 2 complex. An F₁ complementation analysis between allogeneic mice that each reject teratocarcinomas tumors (BALB/c × C57BL/6 and C3H/He × C57BL/6), indicates that the C57BL/6 mice have the 129/Sv tumor-accepting (sensitive) allele at theH-2-linked locus but reject teratocarcinomas because of antigenic differences at a second locus.While these major teratocarcinoma transplantation rejection loci determine the acceptance or rejection of a tumor by a mouse injected with high doses of tumor tissue (750 g of tumor protein), evidence is presented for a number of minor genetic factors that can (1) affect the efficiency of tumor rejection and (2) cause complete tumor rejection at lower tumor doses (7.5–75 g of tumor protein).     

Xenogeneic antisera against T-lymphocyte receptors recognizing allogeneic transplantation antigens: Preparation and properties

Antireceptor sera ARS-1 (anti-CBA-anti-C57BL/6) and ARS-2 (anti-C57BL/6-anti-BALB/c) were prepared in a xenogeneic system by immunizing rabbits with alloimmune CBA anti-C57BL/6 and C57BL/6 anti-BALB/c lymphocytes and subsequent exhaustive absorption of rabbit immune sera with red blood cells, lymphocytes, liver cells, and serum from intact mice. In the cytotoxicity test, both ARS sera lysed only activated T lymphocytes of corresponding, but no other specificities, and did not affect intact lymphocytes. They did not inactivate in vitro the PFC-producing antibodies to SRBC or inhibit the immune response to SRBC and Viantigen of Salmonella typhi in adoptive transfer experiments. Pretreatment of intact CBA lymphocytes in vitro with ARS-1 plus complement suppressed their ability to induce lethal GvH disease in irradiated (CBA × C57BL/6)F₁, but not (CBA × BALB/c)F₁ recipients; similar pretreatment of C57BL/6 lymphocytes did not lower lethality among irradiated (CBA × C57BL/6)F₁ recipients. This method of preparing ARS may help to obtain highly specific antireceptor sera for regulation of the immune response to different antigens in outbred animals and in humans.     

Foxp3+ Regulatory T Cells Delay Expulsion of Intestinal Nematodes by Suppression of IL-9-Driven Mast Cell Activation in BALB/c but Not in C57BL/6 Mice

Accumulating evidence suggests that IL-9-mediated immunity plays a fundamental role in control of intestinal nematode infection. Here we report a different impact of Foxp3⁺ regulatory T cells (Treg) in nematode-induced evasion of IL-9-mediated immunity in BALB/c and C57BL/6 mice. Infection with Strongyloides ratti induced Treg expansion with similar kinetics and phenotype in both strains. Strikingly, Treg depletion reduced parasite burden selectively in BALB/c but not in C57BL/6 mice. Treg function was apparent in both strains as Treg depletion increased nematode-specific humoral and cellular Th2 response in BALB/c and C57BL/6 mice to the same extent. Improved resistance in Treg-depleted BALB/c mice was accompanied by increased production of IL-9 and accelerated degranulation of mast cells. In contrast, IL-9 production was not significantly elevated and kinetics of mast cell degranulation were unaffected by Treg depletion in C57BL/6 mice. By in vivo neutralization, we demonstrate that increased IL-9 production during the first days of infection caused accelerated mast cell degranulation and rapid expulsion of S. ratti adults from the small intestine of Treg-depleted BALB/c mice. In genetically mast cell-deficient (Cpa3-Cre) BALB/c mice, Treg depletion still resulted in increased IL-9 production but resistance to S. ratti infection was lost, suggesting that IL-9-driven mast cell activation mediated accelerated expulsion of S. ratti in Treg-depleted BALB/c mice. This IL-9-driven mast cell degranulation is a central mechanism of S. ratti expulsion in both, BALB/c and C57BL/6 mice, because IL-9 injection reduced and IL-9 neutralization increased parasite burden in the presence of Treg in both strains. Therefore our results suggest that Foxp3⁺ Treg suppress sufficient IL-9 production for subsequent mast cell degranulation during S. ratti infection in a non-redundant manner in BALB/c mice, whereas additional regulatory pathways are functional in Treg-depleted C57BL/6 mice.     

Modeling Susceptibility versus Resistance in Allergic Airway Disease Reveals Regulation by Tec Kinase Itk

Murine models of allergic asthma have been used to understand the mechanisms of development and pathology in this disease. In addition, knockout mice have contributed significantly to our understanding of the roles of specific molecules and cytokines in these models. However, results can vary significantly depending on the mouse strain used in the model, and in particularly in understanding the effect of specific knockouts. For example, it can be equivocal as to whether specific gene knockouts affect the susceptibility of the mice to developing the disease, or lead to resistance. Here we used a house dust mite model of allergic airway inflammation to examine the response of two strains of mice (C57BL/6 and BALB/c) which differ in their responses in allergic airway inflammation. We demonstrate an algorithm that can facilitate the understanding of the behavior of these models with regards to susceptibility (to allergic airway inflammation) (S_aai) or resistance (R_aai) in this model. We verify that both C57BL/6 and BALB/c develop disease, but BALB/c mice have higher S_aai for development. We then use this approach to show that the absence of the Tec family kinase Itk, which regulates the production of Th2 cytokines, leads to R_aai in the C57BL/6 background, but decreases S_aai on the BALB/c background. We suggest that the use of such approaches could clarify the behavior of various knockout mice in modeling allergic asthma.     

Performance of BALB/c and C57BL/6 mice under an incremental repeated acquisition of behavioral chains procedure

BALB/c (n = 8) and C57BL/6 (n = 11) male mice were trained under an incremental repeated acquisition (IRA) procedure using two distinct training procedures: forward and backward chaining. A new metric for assessing progress on the IRA procedure, progress quotient (PQ), quantified progress as the product of chain length and number of reinforcers earned during a session divided by the total number of reinforcers earned. BALB/c mice progressed further, had higher overall responding, earned more reinforcers, and acquired the response sequences faster than the C57BL/6 mice on both training procedures. There were only minimal effects of training procedure for either strain. The strain differences found between BALB/c and C57BL/6 mice confirm the importance of genetic background to behavior. C57BL/6 mice may be deficient in learning as compared with BALB/c mice but other contributing factors probably include overall responding, motivation, and more rapid satiation or habituation to sucrose reinforcement by the C57BL/6 mice. PQ is a sensitive and valid measure of progress for use in studies of mastery-based incremental repeated acquisition and BALB/c mice perform this challenging learning task better than do C57BL/6 mice.     

Comparative analysis of clinics,pathologies and immune responses in BALB/c and C57BL/6 mice infected with Streptobacillus moniliformis

Streptobacillus (S.) moniliformis is a rat-associated zoonotic pathogen that occasionally causes disease in other species. We investigated the working hypothesis that intranasal infection might lead to different immune responses in C57BL/6 and BALB/c mice associated with distinct pathologies. This study confirmed with 75% mortality the known high susceptibility of C57BL/6 mice to Streptobacillus moniliformis infection in comparison to BALB/c mice which did not develop signs of disease. Main pathologies in C57BL/6 mice were purulent to necrotizing lymphadenitis and pneumonia. Significant seroconversion was recorded in surviving mice of both strains. Differentiation of IgG-subclasses revealed mean ratios of IgG2b to IgG1 below 0.5 in sera of all mice prior to infection and of BALB/c mice post infection. In contrast, C57BL/6 mice had a mean IgG2b/IgG1 ratio of 2.5 post infection indicating a Th1 immune response in C57BL/6 versus a Th2 response in BALB/c mice. Evaluation of different sentinel systems revealed that cultural and serological investigations of these animals might not be sufficient to detect infection. In summary, an intranasal S. moniliformis infection model in C57BL/6 mice leading to purulent to necrotizing inflammations in the lung, the lymph nodes and other organs associated with a Th1 immune response is described.     

Mouse Strain-Dependent Differences in Estrogen Sensitivity During Vaginal Candidiasis

The animal models available for studying the immune response to genital tract infection require induction of a pseudo estrous state, usually achieved by administration of 17-β-estradiol. In our experimental model of vaginal candidiasis, under pseudo estrus, different strains of mice were used. We observed major differences in the clearance of Candida albicans infection among the different strains, ascribable to differing susceptibility to estradiol treatment. In the early phase of infection CD1, BALB/c, C57BL/6 albino and C57BL/6 mice were colonized to similar levels, while in the late phase of infection, BALB/c mice, which are considered genetically resistant to C. albicans infection, exhibited greater susceptibility to vaginal candidiasis than CD1 and C57BL/6 albino strains of mice. This was because estradiol induced “per se” enlarged and fluid-filled uteri, more pronounced in infected mice and consistently more evident in BALB/c and C57BL/6 mice than in CD1 mice. Unlike CD1, BALB/c and C57BL/6 mice showed a heavy fungal colonization of the uterus, even though C57BL/6 mice apparently cleared C. albicans from the vagina. The presence of C. albicans in the vagina and uterus was accompanied by a heavy bacterial load. Collectively these observations prompted us to carry out a careful analysis of estradiol effects in a mouse model of vaginal infection.     

T-cell neoplasm induced by subcutaneous transplantation of a plasmacytoma: characterization of tumor cells.

Thymocytes, isolated 6 days following subcutaneous (sc) transplantation of BALB/c MOPC-315 plasmacytoma into F₁ (BALB/c × C57BL) hybrid mice, when injected sc into normal syngeneic mice, caused the development of a solid sc tumor. The cells of the newly developed tumor were of a mixed population of θ⁺F₁ (BALB/c × C57BL) and θ^? BALB/c cells (approximately 1:1), which represents a new type of mixed T cell-plasma cell neoplasm. Efforts were made to isolate the transformed thymocytes (θ⁺) from the plasmacytoma (θ^?) cells in the new tumor, exploiting differences in their surface properties. Treatment of the mixed tumor cell population with peanut agglutinin (PNA) revealed that only the T tumor cells were agglutinated. The agglutinated cells were recovered after dispersing the clumps with d-galactose (0.15 M) and consisted of 95% θ⁺ cells. The PNA-agglutinated cells were found to induce a similar tumor (85% θ⁺ cells) when injected sc into F₁ (BALB/c × C57BL) mice.     

Separation of T and B lymphocytes from various mouse strains by density gradient electrophoresis

T and B mouse spleen lymphocytes were separated by density gradient electrophoresis on the basis of their surface charge. In all strains examined, the T lymphocytes were found in the high mobility fractions and the B in the low. The T and B cells were separated completely in most fractions, with some overlapping in the middle. Significant differences were found in the electrophoretic distribution profiles between the strains: C57BL/6j, C57BL/10j, (BALB/cXC57BL/6j)F₁, and all the following: B₆·C-H-2^d/cBy (congenic to C57BL/6j), BALB/c, CBA/H/T6j, C57BL/10Sn, and C3H. The C57BL/6j and the (BALB/cXC57BL/6j)F₁ cells appear more heterogeneous as far as electrophoretic mobility is concerned. Almost all the other strains give two major peaks. Moreover, the high mobility areas are less populated in the C57BL/6j and the (BALB/cXC57BL/6j)F₁ animals than in all the others. The above differences were found consistently when cells prepared by different methods were electrophoresed. It is concluded that the surface charge of lymphocytes may be genetically determined. Possible dependency on the H-2 complex or non-H-2 areas is discussed.     

Genetic interactions in induction of endogenous murine leukemia virus from low leukemic mice

The frequency of ecotropic murine leukemia virus (MuLV) production in cells induced with halogenated pyrimidines has been investigated in several low leukemic strains of mice. Very few BALB/c or C57BL/6 (B6) induced embryo cells produce MuLV; this low frequency increases 10 to 50 fold in cells of the BALB/c × B6 F1 hybrid. Data from back-crosses of the F1 hybrid to each parent and from BALB/c × B6 recombinant inbred strains indicate that the phenotype of enhanced MuLV production results from interaction of two unlinked loci, dominant (+/+) alleles of which are carried by either parent. Genetic tests with BALB/c × B6 recombinant inbred strains confirm this two-locus model. The loci are designated Inc-1 and Inb-1 to signify their phenotypic detection by induction and the BALB/c or B6 strain of origin, respectively. Examination of hybrids of BALB/c and of B6 with other strains indicates that strains related in pedigree to BALB/c carry Inc-1, whereas those related to B6 carry Inb-1. Identification of genetic loci that specifically interact to enhance MuLV production after exposure to halogenated pyrimidines indicates the existence of mechanisms that regulate the induction or intracellular expression of endogenous MuLV.     

The Contribution of Natural Killer Complex Loci to the Development of Experimental Cerebral Malaria

Background

The Natural Killer Complex (NKC) is a genetic region of highly linked genes encoding several receptors involved in the control of NK cell function. The NKC is highly polymorphic and allelic variability of various NKC loci has been demonstrated in inbred mice, providing evidence for NKC haplotypes. Using BALB.B6-Cmv1^r congenic mice, in which NKC genes from C57BL/6 mice were introduced into the BALB/c background, we have previously shown that the NKC is a genetic determinant of malarial pathogenesis. C57BL/6 alleles are associated with increased disease-susceptibility as BALB.B6-Cmv1^r congenic mice had increased cerebral pathology and death rates during P. berghei ANKA infection than cerebral malaria-resistant BALB/c controls.

Methods

To investigate which regions of the NKC are involved in susceptibility to experimental cerebral malaria (ECM), intra-NKC congenic mice generated by backcrossing recombinant F2 progeny from a (BALB/c x BALB.B6-Cmv1^r) F1 intercross to BALB/c mice were infected with P. berghei ANKA.

Results

Our results revealed that C57BL/6 alleles at two locations in the NKC contribute to the development of ECM. The increased severity to severe disease in intra-NKC congenic mice was not associated with higher parasite burdens but correlated with a significantly enhanced systemic IFN-γ response to infection and an increased recruitment of CD8⁺ T cells to the brain of infected animals.

Conclusions

Polymorphisms within the NKC modulate malarial pathogenesis and acquired immune responses to infection.     

BCG-mediated protection against Mycobacterium ulcerans infection in the mouse

Background

Vaccination with Mycobacterium bovis bacille Calmette-Guérin (BCG) is widely used to reduce the risk of childhood tuberculosis and has been reported to have efficacy against two other mycobacterial diseases, leprosy and Buruli ulcer caused by M. ulcerans (Mu). Studies in experimental models have also shown some efficacy against infection caused by Mu. In mice, most studies use the C57BL/6 strain that is known to develop good cell-mediated protective immunity. We hypothesized that there may be differences in vaccination efficacy between C57BL/6 and the less resistant BALB/c strain.

Methods

We evaluated BCG vaccine efficacy against challenge with ∼3×10⁵ M. ulcerans in the right hind footpad using three strains: initially, the Australian type strain, designated Mu1617, then, a Malaysian strain, Mu1615, and a recent Ghanaian isolate, Mu1059. The latter two strains both produce mycolactone while the Australian strain has lost that capacity. CFU of both BCG and Mu and splenocyte cytokine production were determined at intervals after infection. Time to footpad swelling was assessed weekly.

Principal Findings

BCG injection induced visible scars in 95.5% of BALB/c mice but only 43.4% of C57BL/6 mice. BCG persisted at higher levels in spleens of BALB/c than C57BL/6 mice. Vaccination delayed swelling and reduced Mu CFU in BALB/c mice, regardless of challenge strain. However, vaccination was only protective against Mu1615 and Mu1617 in C57BL/6 mice. Possible correlates of the better protection of BALB/c mice included 1) the near universal development of BCG scars in these mice compared to less frequent and smaller scars observed in C57BL/6 mice and 2) the induction of sustained cytokine, e.g., IL17, production as detected in the spleens of BALB/c mice whereas cytokine production was significantly reduced, e.g., IL17, or transient, e.g., Ifnγ, in the spleens of C57BL/6 mice.

Conclusions

The efficacy of BCG against M. ulcerans, in particular, and possibly mycobacteria in general, may vary due to differences in both host and pathogen.     

No recombinations between Tcra-V and Tcra-C gene segments in 669 backcross mice

Because T-cell receptor (Tcr) genes may possibly function as non-major histocompatibility complex (MHC) immune response genes or predispose for autoimmune diseases, it is important to know how these genes are inherited. We found that Bgl I-digested DNA of BALB/c, C3H, DBA/2, and C57BL/6 exhibited restriction enzyme fragment length polymorphisms (RFLPs) for the Tcra-V1, Tcra-V2, Tcra-V4, Tcra-V6, Tcra-V7, Tcra-V8, Tcra-V11, Tcra-122, Tcra-V13, and Tcra-C gene segments. Inheritance of these RFLPs in 669 offspring from (BALB/c × C57BL/6) × BALB/c, (BALB/c × C57BL/6) × C57BL/6, (C57BL/6 × DBA2) × DBA/2, and (C57BL/6 × C3H) × C3H backcrosses was studied. Since we did not find any recombinations in the offspring, Tcra-V and Tcra-C gene segments are tightly linked and inherited as a haplotype. A peculiar finding was that 22 out of 103 (BALB/c × C57BL/6) × BALB/c offspring, heterozygous for Tcra-C, had deleted a C57BL/6 Tcra-V1 band as well as Tcra-V2 and Tcra-V4 bands. As will be discussed, this deletion is probably caused by heterogeneity in the C57BL/6 breeding stock of a commercial supplier. In seven BXD and BXH recombinant inbred strains with known recombinations between the Tcra-C and Es-10 loci, all Tcra-V RFLPs cosegregated with the Tcra-C RFLP. This finding agrees with the conclusion from our backcross studies; namely that Tcra-V and Tcra-C gene segments are tightly linked.     

Comparison of the ease of tolerance induction in thymus and bone marrow of three strains of mice

Three strains of mice which vary in their susceptibility to induction of immune tolerance with human gamma-globulin were studied to evaluate the cellular basis for their sensitivity to induction of the unresponsive state. Tolerance induction in BALB/c mice was difficult to establish, while tolerance induction was easily achieved in C57BL/6 and CBF₁ (BALB/c × C57BL/6) mice. The degree of unresponsiveness obtained with various tolerogen doses in intact C57BL/6 and CBF₁ mice was reflected in the sensitivity of their thymocytes to the production of the unresponsive state. In the BALB/c mouse strain slight immune suppression observed at low tolerogen doses was correlated with bone marrow cell unresponsiveness while significant levels of tolerance observed at a high tolerogen dose was due to suppression of thymus cells. It was apparent that CBF₁ mice had inherited both thymus cells and bone marrow cells which exhibited the sensitivity to induction of immune tolerance characteristic of those same cells of their C57BL/6 parent.     

Murine responses to (Tyr-Glu-Ala-Gly)n: II. H-2 and non-H-2 gene effects

Mice of the H-2^b haplotype responded to the sequential polymer poly(Tyr-Glu-Ala-Gly) in the in vitro T-cell proliferative assay, irrespective of whether they were homozygous or heterozygous at the H-2^b locus. The antibody responses of the H-2^b congenic mice to this polymer were variable, with A.BY and BALB.B showing responses better than those of C57BL/6 and C57BL/10 strains. The antibody responses of the F₁ progeny of (responder × nonresponder) strains of mice to this polymer are generally lower than the responder parents. F₁ mice with C57BL/10 background were the poorest responders. Studies with F₂ mice and backcross progenies of selective breeding of high and low antibody responder (C57BL/6 × BALB/c) F₁ to high responder C57BL/6 mice indicated that both non-H-2 genes and H-2 gene dosage effects influenced the magnitude of the humoral antibody responses. Animals having low responder non-H-2 background and only half the dosage of the responder immune response genes has greatly diminished antibody responses.     

Toxoplasma gondii 70 kDa Heat Shock Protein: Systemic Detection Is Associated with the Death of the Parasites by the Immune Response and Its Increased Expression in the Brain Is Associated with Parasite Replication

The heat shock protein of Toxoplasma gondii (TgHSP70) is a parasite virulence factor that is expressed during T. gondii stage conversion. To verify the effect of dexamethasone (DXM)-induced infection reactivation in the TgHSP70-specific humoral immune response and the presence of the protein in the mouse brain, we produced recombinant TgHSP70 and anti-TgHSP70 IgY antibodies to detect the protein, the specific antibody and levels of immune complexes (ICs) systemically, as well as the protein in the brain of resistant (BALB/c) and susceptible (C57BL/6) mice. It was observed higher TgHSP70-specific antibody titers in serum samples of BALB/c compared with C57BL/6 mice. However, the susceptible mice presented the highest levels of TgHSP70 systemically and no detection of specific ICs. The DXM treatment induced increased parasitism and lower inflammatory changes in the brain of C57BL/6, but did not interfere with the cerebral parasitism in BALB/c mice. Additionally, DXM treatment decreased the serological TgHSP70 concentration in both mouse lineages. C57BL/6 mice presented high expression of TgHSP70 in the brain with the progression of infection and under DXM treatment. Taken together, these data indicate that the TgHSP70 release into the bloodstream depends on the death of the parasites mediated by the host immune response, whereas the increased TgHSP70 expression in the brain depends on the multiplication rate of the parasite.