The efferent projections of the periaqueductal gray in the rat: a Phaseolus vulgaris-leucoagglutinin study. I. Ascending projections

This study has examined the ascending projections of the periaqueductal gray in the rat. Injections of Phaseolus vulgaris-leucoagglutinin were placed in the dorsolateral or ventrolateral subregions, at rostral or caudal sites. From either region, fibers ascended via two bundles. The periventricular bundle ascended in the periaqueductal and periventricular gray matter. At the posterior commissure level, this bundle divided into a dorsal component that terminated in the intralaminar and midline thalamic nuclei, and a ventral component that supplied the hypothalamus. The ventral bundle formed in the deep mesencephalic reticular formation and supplied the ventral tegmental area, substantia nigra pars compacta, and the retrorubral field. The remaining fibers were incorporated into the medial forebrain bundle. These supplied the lateral hypothalamus and forebrain structures, including the preoptic area, the nuclei of the diagonal band, and the lateral division of the bed nucleus of the stria terminalis. The dorsolateral subregion preferentially innervated the centrolateral and paraventricular thalamic nuclei and the anterior hypothalamic area. The ventrolateral subregion preferentially innervated the parafascicular and central medial thalamic nuclei, the lateral hypothalamic area, and the lateral division of the bed nucleus of the stria terminalis. Although the dorsolateral and ventrolateral subregions gave rise to differential projections, the projections from both the rostral and caudal parts of either subregion were similar. This suggests that the dorsolateral and ventrolateral subregions are organized into longitudinal columns that extend throughout the length of the periaqueductal gray. These columns may correspond to those demonstrated in recent physiological studies.

The efferent projections of the periaqueductal gray in the rat: a Phaseolus vulgaris-leucoagglutinin study. II. Descending projections

The descending projections of the periaqueductal gray (PAG) have been studied in the rat using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. The tracer was injected into the dorsolateral or ventrolateral subdivisions of the PAG at rostral or caudal sites. It was found that the patterns of the descending projections of the rostral and caudal parts of the dorsolateral PAG were the same and that the patterns of the descending projections of the rostral and caudal parts of the ventrolateral PAG were the same. However, the patterns of projections of the dorsolateral and ventrolateral PAG subregions were substantially different. These results suggest that the dorsolateral and ventrolateral parts of the PAG are organized into longitudinal columns that extend throughout the length of the PAG. The axons of PAG neurons descended through the pons and medulla via two routes. A small fiber bundle was present in the periaqueductal gray and in the periventricular area. This bundle distributed fibers and terminals locally within the periaqueductal gray and in the locus coeruleus and Barrington's nucleus. A larger bundle had a diffuse arrangement in the pontine reticular formation, however, and it had a more restricted distribution in the medulla, where it occupied a position dorsolateral to the pyramid. This bundle supplied structures in the pontine and medullary tegmentum. The dorsolateral column preferentially supplied the locus coeruleus, subcoeruleus, the gigantocellular nucleus pars alpha, the rostral part of the paragigantocellular nucleus, and the region of the A5 noradrenergic cell group. The ventrolateral column preferentially supplied the nucleus raphe magnus, the caudal part of the lateral paragigantocellular nucleus, and the rostroventrolateral reticular nucleus.

Therapy of multidrug-resistant typhoid fever with oral cefixime vs. intravenous ceftriaxone

We randomly allocated 80 children with suspected multidrug-resistant tyhpoid fever to therapy with either cefixime or ceftriaxone. Of these, an alternative diagnosis was subsequently made in 10 children and another 10 were excluded because cultures were negative. In 9 cases the typhoidal organisms isolated were susceptible to first-line drugs. In all, 50 children were randomly allocated to receive therapy with either intravenous ceftriaxone (65 mg/kg/day once daily, Group A, n = 25) or oral cefixime (10 mg/kg/day divided every 12 hours, Group B, n = 25) for 14 days. The two groups were comparable in their clinical characteristics, duration and severity of illness at the time of admission. The time to defervescence was comparable in both groups (8.3 +/- 3.7 vs. 8.0 +/- 4.1 days, P = not significant). An equal number (3 in each group) failed to respond and underwent a change in therapy. Three children in Group A and one in Group B relapsed. No adverse effects were seen in either group during the course of therapy. Our data suggest that oral cefixime can be used as effectively as parenterally administered ceftriaxone for management of typhoid fever in children.

Toxoplasma gondii: a monoclonal antibody that inhibits intracellular replication

During its intracellular life cycle within the infected host cell, Toxoplasma gondii is able to undergo rapid asexual replication. Neither the mechanism by which the parasite initiates this process nor the requirements for maintaining it are understood. We produced a monoclonal antibody, 1B8, that identifies a parasite antigen of approximate M(r) 97 kDa as determined by SDS-PAGE. The epitope recognized by mAb 1B8 appears as a collection of vesicular structures scattered throughout the cell cytoplasm. When RH strain parasites are incubated with mAb 1B8 in the absence of serum complement, parasite growth is inhibited by > 90% as determined by radioisotope incorporation. Both attachment and invasion assays show that neither of these parasite-host cell interactions are inhibited by the mAb. However, a marked reduction in the number of intracellular rosettes was observed following mAb treatment of the parasites. Viable extracellular parasites are able to endocytose mAb 1B8. Once within the parasite cytosol the antibody recognizes the vesicular structures similar to those observed with fixed parasites. Immunofluorescence assays with Besnoitia jellisoni and Plasmodium falciparum show that the epitope recognized by mAb 1B8 is conserved among Coccidiae but not the kinetoplastid Leishmania.

Seasonal and daily variations in the plasma gonadotropin II response to a LHRH analog and serotonin in Atlantic croaker (Micropogonias undulatus): evidence for mediation by 5-HT2 receptors

The effects of serotonin (5-hydroxytryptamine; 5-HT) alone, and in combination with luteinizing hormone-releasing hormone analog (LHRHa), on plasma levels of maturational gonadotropin (GtH II) in the post-vitellogenic female and spermiating male Atlantic croaker were investigated during mid-light, late-light, mid-dark, and late-dark phases of the day-night (12 hr light: 12 hr dark) cycle. Although LHRHa stimulated GtH II secretion throughout the day-night cycle, maximal stimulation was observed during the mid-dark phase. Serotonin significantly potentiated LHRHa-induced GtH II secretion at all time points tested except during the late-dark phase. The plasma GtH II response to LHRHa was markedly reduced, and the response to 5-HT was abolished in regressed Atlantic croaker. Pretreatment of the fish with a 5-HT2 antagonist, LY 53,857 maleate, almost completely abolished the stimulatory effect of 5-HT on LHRHa-induced GtH II secretion, whereas a 5-HT1 antagonist, methiothepin mesylate, failed to influence the stimulatory effect of 5-HT on GtH II secretion. In addition, a 5-HT2 agonist, (+/-) DOI hydrochloride, potentiated the effect of 5-HT on basal and LHRHa-induced GtH II secretion, while a 5-HT1 agonist, m-chlorophenylpiperazine dihydrochloride, did not. The results clearly demonstrate time- and season-dependent stimulatory effects of LHRHa and 5-HT on plasma GtH II levels in Atlantic croaker. Moreover, the stimulatory effect of 5-HT appears to be mediated by 5-HT2 receptors in this species.

A single aspartate residue is involved in both intrinsic gating and blockage by Mg2+ of the inward rectifier, IRK1

1. We describe the effects on channel function of changing an aspartate residue (Asp172) in a membrane-spanning alpha-helix of the murine inward rectifier, IRK1, by site-directed mutagenesis. 2. Alteration of Asp172 to Glu (charged) or to Gln or Asn (polar but uncharged) produced functional channels showing inward rectification, though rectification was weaker with Gln and Asn. 3. Intrinsic gating around the potassium equilibrium potential, EK, was conserved only if the charge on residue 172 was conserved. Currents through channels with Gln or Asn in this position showed no time dependence under hyperpolarization. 4. The change from Asp to Gln also reduced the affinity for internal Mg2+ at least fivefold, indicating that Asp172 also forms part of the site for Mg2+ blockage. 5. The consequences for channel structure of Asp172 lining the pore are discussed.

Interleukin-12 enhances murine survival against acute toxoplasmosis

Protective immunity against Toxoplasma gondii is mediated by the host cellular immune response. Interleukin-12 (IL-12), a recently described cytokine that stimulates NK cells to produce gamma interferon (IFN-gamma), is able to enhance host protection against this parasite in SCID mice. Administration of IL-12 to A/J mice significantly increased survival over that of control mice when IL-12 was delivered early in the course of acute infection. If it was administered at day 3 or thereafter, there was no observed difference in mortality between treated and control mice. Antibody depletion of IL-12 increased susceptibility to infection, as measured by mortality, only when the IL-12 was administered before day 3 postinfection. Mice treated with IL-12 at day 0 postinfection exhibited a significant rise above the control in both IL-2 and IFN-gamma production. Once infection has been established in the host (3 days), administration of exogenous IL-12 is unable to alter parasite-induced downregulation of IFN-gamma production. Thus, IL-12 appears to play an important, but transitory, role in protection against acute infection with T. gondii in the normal murine host.

Antigen-specific CD8+ T cell clone protects against acute Toxoplasma gondii infection in mice

Encephalitis caused by the obligate intracellular protozoan, Toxoplasma gondii, is a major cause of morbidity and mortality in those afflicted with AIDS. The cell-mediated response is critical for host immunity against this parasite. A panel of T cell clones that proliferate in response to a major parasite protein, p30 (SAG-1) were isolated from mice. One of these clones (C3) bearing the CD8+ phenotype was able to induce nearly 100% protection against acute infection when adoptively transferred into naive mice. In contrast, an Ag-specific CD4+ T cell clone (C2) failed to show significant protection in spite of its ability to produce similar quantities of IFN-gamma. Depletion of host CD4+ T cells with mAb had no effect on CD8(+)-mediated adoptive protection, whereas treatment with anti-IFN-gamma completely abrogated this protection. These results indicate that Ag-specific CD8+ T cells in combination with IFN-gamma are able to induce significant protection against acute toxoplasmosis in the experimental murine model.

The intrinsic gating of inward rectifier K+ channels expressed from the murine IRK1 gene depends on voltage, K+ and Mg2+

1. We describe the cloning of the inward rectifier K+ channel IRK1 from genomic DNA of mouse; the gene is intronless. 2. The IRK1 gene can be stably expressed in murine erythroleukaemia (MEL) cells. Such transfected cells show inward rectification under whole-cell recording. 3. Channels encoded by the IRK1 gene have an intrinsic gating that depends on voltage and [K+]o. Rate constants are reduced e-fold as the driving force on K+(V-EK) is reduced by 24.1 mV. 4. Removal of intracellular Mg2+ permits brief outward currents under depolarization. The instantaneous current-voltage relation may be fitted by an appropriate constant field expression. 5. Removal of intracellular Mg2+ speeds channel closure at positive voltages. In nominally zero [Mg2+]i, rate constants for the opening and closing of channels, processes which are first order, are similar to those of native channels.

Antigen-specific CD8+ T cell clone protects against acute Toxoplasma gondii infection in mice

Encephalitis caused by the obligate intracellular protozoan, Toxoplasma gondii, is a major cause of morbidity and mortality in those afflicted with AIDS. The cell-mediated response is critical for host immunity against this parasite. A panel of T cell clones that proliferate in response to a major parasite protein, p30 (SAG-1) were isolated from mice. One of these clones (C3) bearing the CD8+ phenotype was able to induce nearly 100% protection against acute infection when adoptively transferred into naive mice. In contrast, an Ag-specific CD4+ T cell clone (C2) failed to show significant protection in spite of its ability to produce similar quantities of IFN-gamma. Depletion of host CD4+ T cells with mAb had no effect on CD8(+)-mediated adoptive protection, whereas treatment with anti-IFN-gamma completely abrogated this protection. These results indicate that Ag-specific CD8+ T cells in combination with IFN-gamma are able to induce significant protection against acute toxoplasmosis in the experimental murine model.

Broad resistance to tobamoviruses is mediated by a modified tobacco mosaic virus replicase transgene

Tobacco plants made transgenic to express the wild type tobacco mosaic virus (TMV) 183-kDa replicase gene were not resistant to TMV. However, transgenic plants containing essentially the same sequences, but with an additional insertion that would terminate translation in the middle of the 183-kDa gene, were highly resistant to systemic infection by TMV and other tobamoviruses. The 1.4-kbp insertion in the replicase open reading frame (ORF) of the resistant plants was shown by DNA sequencing to be an IS10-like transposable element, which apparently inserted itself into the TMV sequence at nucleotide 2875 sometime during the propagation of this replicase ORF plasmid (pREP21). Because of four stop codons, in frame with the TMV replicase ORF on the immediate 5' border of the IS insertion, REP21 effectively represents domain 1 (putative methylase domain) and a portion of domain 2 (putative helicase domain) of the TMV replicase ORF. REP21 Xanthi tobacco plants had a level of resistance to TMV similar to other reported transgenic replicase plants. No TMV was detected in upper leaves of these plants at 1-mo postinoculation. In addition, REP21 plants were resistant to an unusually broad range of tobamoviruses including tomato mosaic virus, tobacco mild green mosaic virus, TMV-U5, green tomato atypical mosaic virus, and ribgrass mosaic virus. These plants were not resistant to cucumber mosaic cucumovirus. The lack of systemic infection by TMV was due to reduced multiplication in inoculated leaves rather than complete prevention of replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of serotonin and gonadotropin-releasing hormone in the brain and pituitary gland of the Atlantic croaker Micropogonias undulatus

The distribution of serotonin-immunoreactive (5-HT-ir) and gonadotropin-releasing hormone-immunoreactive (GnRH-ir) elements in the brain and pituitary gland of the Atlantic croaker (Micropogonias undulatus) was studied using immunoperoxidase and immunofluorescence techniques. 5-HT- and GnRH-ir perikarya were observed in the ventrolateral region of the olfactory bulbs and in the preoptic-anterior hypothalamic area bordering the third ventricle as well as in regions distal to the ependyma of the third ventricle. The immunoreactive elements of the two systems appear to overlap in these regions. Cerebrospinal fluid-contacting 5-HT-ir neurons were found in the periventricular hypothalamus, particularly in the preoptic area and in the nucleus posterior periventricularis, nucleus ventromedialis thalami, nucleus recessus lateralis, and nucleus recessus posterioris. Immunoreactivity to 5-HT in the pituitary was strongest in the proximal pars distalis (PPD) and in a few scattered cells bordering the pars intermedia. Dendritic processes of 5-HT neurons could be seen contacting the adjoining hypophysial cells in the PPD. GnRH-ir fibers were seen entering the pituitary stalk and the immunoreaction was concentrated in the ventral PPD. Several large 5-HT-ir perikarya were located in the raphe region forming a column in the mediosagittal plane. The results suggest that the general organization of the 5-HT system in the brain of the Atlantic croaker is similar to that described in other vertebrates. The demonstration that 5-HT and GnRH systems are in close proximity, particularly in the olfactory bulbs and in the preoptic-anterior hypothalamic area of the croaker brain, suggests that the two systems may interact in these regions of the teleostean brain to control several reproductive functions including spawning behavior and gonadotropin release.

Antibodies to Toxoplasma gondii major surface protein (SAG-1, P30) inhibit infection of host cells and are produced in murine intestine after peroral infection

Monoclonal and polyclonal, monospecific antibodies to the major surface antigen of Toxoplasma gondii (SAG-1, P30) inhibit infection of human fibroblasts and murine enterocytes. Fab prepared from polyclonal, monospecific antibody to P30 also have this inhibitory effect on invasion, which indicates that this antibody directly blocks parasite infection of host cells rather agglutinating the parasite. Antibodies to another surface protein (P22) did not alter in vitro infection. If the inhibitory effect of antibody to P30 was due to steric hindrance or complexing of surface epitopes contiguous to P30, antibodies to other surface epitopes would also be inhibitory and they are not. Urea treatment of antibody (which permits discrimination of high and low avidity antibody) did not alter the effect of anti-P30 antibody. This observation indicates that the effect of the antibody to P30 was not an artifact of differences in the avidity of the antibody to P22 and P30. Heat inactivated antisera from mice infected with either RH or PTg strain T. gondii (P30+) inhibit infection of fibroblasts when challenged with autologous wild-type parasites by 87 and 40%, respectively. In contrast, these antisera have little inhibitory effect (13 and 19%, respectively) against infection of human fibroblasts by a P30-deficient mutant (PTgB). Antisera raised to the P30-deficient mutant had no significant effect on infection of cells by wild-type strains that have surface P30. The neoglycoprotein, BSA-glucosamide, competitively blocks infection of human fibroblasts by P30+ tachyzoites with surface P30 in higher level than those without surface P30. This observation indicates that there is likely to be a glycosylated host cell receptor to which T. gondii's major surface Ag SAG-1 (P30) binds. Mice infected perorally develop intestinal IgA antibody to the major 30-kDa epitope of T. gondii. Thus, the major surface epitope of T. gondii, SAG-1 (P30), has an important, functional role in infection of host cells by T. gondii and elicits an intestinal antibody response after peroral infection.

Antibodies to Toxoplasma gondii major surface protein (SAG-1, P30) inhibit infection of host cells and are produced in murine intestine after peroral infection

Monoclonal and polyclonal, monospecific antibodies to the major surface antigen of Toxoplasma gondii (SAG-1, P30) inhibit infection of human fibroblasts and murine enterocytes. Fab prepared from polyclonal, monospecific antibody to P30 also have this inhibitory effect on invasion, which indicates that this antibody directly blocks parasite infection of host cells rather agglutinating the parasite. Antibodies to another surface protein (P22) did not alter in vitro infection. If the inhibitory effect of antibody to P30 was due to steric hindrance or complexing of surface epitopes contiguous to P30, antibodies to other surface epitopes would also be inhibitory and they are not. Urea treatment of antibody (which permits discrimination of high and low avidity antibody) did not alter the effect of anti-P30 antibody. This observation indicates that the effect of the antibody to P30 was not an artifact of differences in the avidity of the antibody to P22 and P30. Heat inactivated antisera from mice infected with either RH or PTg strain T. gondii (P30+) inhibit infection of fibroblasts when challenged with autologous wild-type parasites by 87 and 40%, respectively. In contrast, these antisera have little inhibitory effect (13 and 19%, respectively) against infection of human fibroblasts by a P30-deficient mutant (PTgB). Antisera raised to the P30-deficient mutant had no significant effect on infection of cells by wild-type strains that have surface P30. The neoglycoprotein, BSA-glucosamide, competitively blocks infection of human fibroblasts by P30+ tachyzoites with surface P30 in higher level than those without surface P30. This observation indicates that there is likely to be a glycosylated host cell receptor to which T. gondii's major surface Ag SAG-1 (P30) binds. Mice infected perorally develop intestinal IgA antibody to the major 30-kDa epitope of T. gondii. Thus, the major surface epitope of T. gondii, SAG-1 (P30), has an important, functional role in infection of host cells by T. gondii and elicits an intestinal antibody response after peroral infection.

Stimulatory effects of serotonin on maturational gonadotropin release in the Atlantic croaker, Micropogonias undulatus

The effects of serotonin (5-HT) injection alone, and in combination with des Gly10 [D-Trp6]-luteinizing hormone-releasing hormone ethylamide (LHRHa), on plasma maturational gonadotropin (GtH) levels in the Atlantic croaker, Micropogonias undulatus, were examined. An injection of 5-HT (20 micrograms/g body wt) alone did not significantly elevate GtH levels, whereas simulatneous administration of LHRHa (20 ng/g body wt) and 5-HT elicited a greater elevation of plasma GtH levels than that induced by LHRHa alone. Pretreatment of 1-year-old fish with fluoxetine (10 micrograms/g), a 5-HT reuptake inhibitor, only slightly augmented the effect of 5-HT on GtH levels, whereas pretreatment with ketanserin (10 micrograms/g), a 5-HT receptor antagonist, completely inhibited the potentiating effect of 5-HT on the GtH response to LHRHa. Administration of LHRHa (20 ng/g) or 5-HT (20 micrograms/g) significantly elevated GtH levels in the 2- and 3-year-old croaker, but the combined treatment failed to increase GtH levels above those induced by LHRHa alone. However, with a lower dose of LHRHa (5 ng/g), the combination produced an additive effect. Serotonin (20 micrograms/ml media) alone, and in combination with LHRHa (10 ng/ml media), significantly stimulated GtH release from the pituitaries of gonadally mature 2- and 3-year-old female croaker during an 18-hr incubation in vitro, but not from pituitaries of gonadally regressed fish. The combined treatment of LHRHa with 5-HT also significantly stimulated in vitro GtH release during 6- and 12-hr pituitary incubations, whereas these treatments alone were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigen-specific (p30) mouse CD8+ T cells are cytotoxic against Toxoplasma gondii-infected peritoneal macrophages

The importance of CD8+ T cells in immunity against Toxoplasma gondii is now well recognized. The mechanism by which these CD8+ T cells are able to confer this immunity is not yet understood. To examine the Ag specificity of this response, immune splenocytes from mice immunized with p30, a major surface parasite Ag, were evaluated for their ability to lyse peritoneal macrophages infected with three different strains of T. gondii. Macrophages infected with either the RH or P wild-type strain tachyzoites were lysed at varying E:T ratios by nylon wool nonadherent immune splenocytes whereas macrophages infected with a p30-deficient mutant (B mutant) of the P strain were not. The gene encoding p30 for the wild type and B mutant were amplified by the polymerase chain reaction. This revealed a nonsense mutation in the B mutant such that its primary translation product is predicted to be about two-thirds the size of the wild-type p30 molecule. mAb depletion studies indicate that the cytotoxic effect of the immune splenocytes is mediated by the CD8+ T cell population. Peritoneal macrophages infected with the three different strains (RH, P wild type, B mutant) from mice genetically restricted were not lysed by the immune CD8+ effector cell population. A cloned line (C3) of p30 Ag-specific CD8+ T cells exhibited significant cytotoxicity against syngeneic peritoneal macrophages infected with either the RH or P strain tachyzoites. There was no macrophage lysis observed by these CD8+ effector cells of either syngeneic macrophages infected with the B mutant or nonsyngeneic macrophages infected with the three different tachyzoite strains.

Antigen-specific (p30) mouse CD8+ T cells are cytotoxic against Toxoplasma gondii-infected peritoneal macrophages

The importance of CD8+ T cells in immunity against Toxoplasma gondii is now well recognized. The mechanism by which these CD8+ T cells are able to confer this immunity is not yet understood. To examine the Ag specificity of this response, immune splenocytes from mice immunized with p30, a major surface parasite Ag, were evaluated for their ability to lyse peritoneal macrophages infected with three different strains of T. gondii. Macrophages infected with either the RH or P wild-type strain tachyzoites were lysed at varying E:T ratios by nylon wool nonadherent immune splenocytes whereas macrophages infected with a p30-deficient mutant (B mutant) of the P strain were not. The gene encoding p30 for the wild type and B mutant were amplified by the polymerase chain reaction. This revealed a nonsense mutation in the B mutant such that its primary translation product is predicted to be about two-thirds the size of the wild-type p30 molecule. mAb depletion studies indicate that the cytotoxic effect of the immune splenocytes is mediated by the CD8+ T cell population. Peritoneal macrophages infected with the three different strains (RH, P wild type, B mutant) from mice genetically restricted were not lysed by the immune CD8+ effector cell population. A cloned line (C3) of p30 Ag-specific CD8+ T cells exhibited significant cytotoxicity against syngeneic peritoneal macrophages infected with either the RH or P strain tachyzoites. There was no macrophage lysis observed by these CD8+ effector cells of either syngeneic macrophages infected with the B mutant or nonsyngeneic macrophages infected with the three different tachyzoite strains.

Tubulin structure and biochemistry

In the past year, much has been learned about structure-function correlations in the tubulin molecule, and specifically about the nature and roles of post-translational modifications and tubulin isotypes. The interactions between tubulin and its ligands--both microtubule-associated proteins and anti-mitotic drugs--are becoming clearer at the molecular level.

A purified parasite antigen (p30) mediates CD8+ T cell immunity against fatal Toxoplasma gondii infection in mice

Induction of protective immunity against acute and chronic toxoplasmosis can be achieved using p30, the major membrane and excreted/secreted protein of Toxoplasma gondii. This protein, when administered to outbred mice in the presence of the saponin Quil A, is able to induce almost 100% protection against acute infection without evidence of intracerebral cyst development. Adoptive transfer of immune splenocytes from immunized inbred A/J mice conferred a significant level (p less than 0.001) of protection against subsequent challenge. Phenotypic analysis in outbred as well as two different strains of inbred mice (A/J and C57BL/6) demonstrated that CD8+ T cells are selectively stimulated by this immunization protocol. T cell depletion studies using specific mAb directed at either CD3+ or CD8+ T cell phenotype, followed by adoptive transfer, failed to confer protective immunity, whereas CD4+ depletion had no effect. These cytotoxic CD8+ T cells produced high titers of both IFN-gamma and IL-2. Moreover, these CD8+ T cells were directly parasiticidal against radiolabeled extracellular T. gondii, further supporting the critical immune function of these p30 Ag-specific CD8+ T cells in host immunity against T. gondii infection.

A purified parasite antigen (p30) mediates CD8+ T cell immunity against fatal Toxoplasma gondii infection in mice

Induction of protective immunity against acute and chronic toxoplasmosis can be achieved using p30, the major membrane and excreted/secreted protein of Toxoplasma gondii. This protein, when administered to outbred mice in the presence of the saponin Quil A, is able to induce almost 100% protection against acute infection without evidence of intracerebral cyst development. Adoptive transfer of immune splenocytes from immunized inbred A/J mice conferred a significant level (p less than 0.001) of protection against subsequent challenge. Phenotypic analysis in outbred as well as two different strains of inbred mice (A/J and C57BL/6) demonstrated that CD8+ T cells are selectively stimulated by this immunization protocol. T cell depletion studies using specific mAb directed at either CD3+ or CD8+ T cell phenotype, followed by adoptive transfer, failed to confer protective immunity, whereas CD4+ depletion had no effect. These cytotoxic CD8+ T cells produced high titers of both IFN-gamma and IL-2. Moreover, these CD8+ T cells were directly parasiticidal against radiolabeled extracellular T. gondii, further supporting the critical immune function of these p30 Ag-specific CD8+ T cells in host immunity against T. gondii infection.