Wound zygomycosis: two cases with unusual manifestations.
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Adult↗
Biomedical subjects
R Ahmed
Publications and source records attributed to R Ahmed.
Interleukin-4 acts at the locus of the antigen-presenting dendritic cell to counter-regulate cytotoxic CD8+ T-cell responses.
The mechanism underlying suppression of immune responses by interleukin-4 (IL-4) has remained unexplained. Here we show that the antigen-presenting dendritic cell is central to counter-regulation of autoimmune disease by IL-4. IL-4 acts at the locus of the dendritic cell to decrease the cytolytic T-cell response, preventing autoimmunity. Stimulation of cytotoxic precursors by antigen pulsed dendritic cells induces their differentiation but the process is blocked by IL-4. IL-4-influenced DC produce distinct effects on CD8+ T cells depending on their state of activation. The molecular basis for this regulation is the alteration of the expression ratio of the costimulatory ligands B7.1/B7.2 on dendritic cells. Our findings demonstrate that B7.2 induces expansion of CD8+ T cells and B7.1 governs their acquisition of cytolytic activity. IL-4 influences the dendritic cell to elicit qualitative differences in T-cell responses, providing the basis for counter-regulation mediated by IL-4.
Animals↗
Memory CD8+ T cell differentiation: initial antigen encounter triggers a developmental program in naïve cells.
The rules that govern memory T cell differentiation are not well understood. This study shows that after antigenic stimulation naïve CD8+ T cells become committed to dividing at least seven times and differentiating into effector and memory cells. Once the parental naïve CD8+ T cell had been activated, this developmental process could not be interrupted and the daughter cells continued to divide and differentiate in the absence of further antigenic stimulation. These data indicate that initial antigen encounter triggers an instructive developmental program that does not require further antigenic stimulation and does not cease until memory CD8+ T cell formation.
Adoptive Transfer↗
The economy of T-cell memory: CD4+ recession in times of CD8+ stability?
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Animals↗
Characterization of Salmonella associated with pig ear dog treats in Canada.
In the summer of 1999, the incidence of Salmonella enterica serotype Infantis infections in Alberta rose dramatically. Subsequent laboratory and epidemiological investigations established that an outbreak of human disease caused by this organism was occurring across Canada and was associated with pet treats for dogs produced from processed pig ears. Laboratory investigations using phage typing and pulsed-field gel electrophoresis (PFGE) established that isolates of Salmonella serotype Infantis from pig ear pet treats and humans exposed to pig ear pet treats comprised a well-defined subset of all isolates analyzed. Of the 53 subtypes of Salmonella serotype Infantis obtained around the time of the outbreak as defined by PFGE and phage typing, only 6 subtypes were associated with both human infection and isolation from pig ears. Together with information from epidemiological studies, these investigations established pig ear pet treats as the cause of the Salmonella serotype Infantis outbreak. The results are consistent with a model in which contaminated pig ear pet treats constitute a long-term, continuing vehicle for infection of the human population rather than causing temporally delimited point-source outbreaks. During the course of this outbreak, several other Salmonella serotypes were also isolated from pet treats, suggesting these products may be an important source of enteric infection in both humans and dogs. Though isolates of Salmonella serotypes other than Salmonella serotype Infantis from pet treats were also subjected to PFGE and phage typing, no link with human disease could be definitively established, and the contribution of pig ear pet treats to human disease remains unclear. Elimination of bacterial contamination from pet treats is required to reduce the risk of infection from these products.
Alberta↗
Passive transfer of antibodies protects immunocompetent and imunodeficient mice against lethal Ebola virus infection without complete inhibition of viral replication.
Ebola hemorrhagic fever is a severe, usually fatal illness caused by Ebola virus, a member of the filovirus family. The use of nonhomologous immune serum in animal studies and blood from survivors in two anecdotal reports of Ebola hemorrhagic fever in humans has shown promise, but the efficacy of these treatments has not been demonstrated definitively. We have evaluated the protective efficacy of polyclonal immune serum in a mouse model of Ebola virus infection. Our results demonstrate that mice infected subcutaneously with live Ebola virus survive infection and generate high levels of anti-Ebola virus immunoglobulin G (IgG). Passive transfer of immune serum from these mice before challenge protected upto 100% of naive mice against lethal Ebola virus infection. Protection correlated with the level of anti-Ebola virus IgG titers, and passive treatment with high-titer antiserum was associated with a delay in the peak of viral replication. Transfer of immune serum to SCID mice resulted in 100% survival after lethal challenge with Ebola virus, indicating that antibodies alone can protect from lethal disease. Thus antibodies suppress or delay viral growth, provide protection against lethal Ebola virus infection, and may not require participation of other immune components for protection.
Animals↗
In vivo selection of a lymphocytic choriomeningitis virus variant that affects recognition of the GP33-43 epitope by H-2Db but not H-2Kb.
CD8 T cells drive the protective immune response to lymphocytic choriomeningitis virus (LCMV) infection and are thus a determining force in the selection of viral variants. To examine how escape mutations affect the presentation and recognition of overlapping T-cell epitopes, we isolated an LCMV variant that is not recognized by T-cell receptor (TCR)-transgenic H-2Db-restricted LCMV GP33-41-specific cytotoxic T lymphocytes (CTL). The variant virus carried a single-amino-acid substitution (valine to alanine) at position 35 of the viral glycoprotein. This region of the LCMV glycoprotein encodes both the Db-restricted GP33-43 epitope and a second epitope (GP34-42) presented by the Kb molecule. We determined that the V-to-A CTL escape mutant failed to induce a Db GP33-43-specific CTL response and that Db-restricted GP33-43-specific CTL induced by the wild-type LCMV strain were unable to kill target cells infected with the variant LCMV strain. In contrast, the Kb-restricted response was much less affected. We found that the V-to-A substitution severely impaired peptide binding to Db but not to Kb molecules. Strikingly, the V-to-A mutation did not change any of the anchor residues, and the dramatic effect on binding was therefore unexpected. The strong decrease in Db binding explains why the variant virus escapes the Db GP33-43-specific response but still elicits the Kb-restricted response. These findings also illustrate that mutations within regions encoding overlapping T-cell epitopes can differentially affect the presentation and recognition of individual epitopes.
Amino Acid Substitution↗
Recruitment times, proliferation, and apoptosis rates during the CD8(+) T-cell response to lymphocytic choriomeningitis virus.
The specific CD8(+) T-cell response during acute lymphocytic choriomeningitis virus (LCMV) infection of mice is characterized by a rapid proliferation phase, followed by a rapid death phase and long-term memory. In BALB/c mice the immunodominant and subdominant CD8(+) responses are directed against the NP118 and GP283 epitopes. These responses differ mainly in the magnitude of the epitope-specific CD8(+) T-cell expansion. Using mathematical models together with a nonlinear parameter estimation procedure, we estimate the parameters describing the rates of change during the three phases and thereby establish the differences between the responses to the two epitopes. We find that CD8(+) cell proliferation begins 1 to 2 days after infection and occurs at an average rate of 3 day(-1), reaching the maximum population size between days 5 and 6 after immunization. The 10-fold difference in expansion to the NP118 and GP283 epitopes can be accounted for in our model by a 3.5-fold difference in the antigen concentration of these epitopes at which T-cell stimulation is half-maximal. As a consequence of this 3.5-fold difference in the epitope concentration needed for T-cell stimulation, the rates of activation and proliferation of T cells specific for the two epitopes differ during the response and in combination can account for the large difference in the magnitude of the response. After the peak, during the death phase, the population declines at a rate of 0.5 day(-1), i.e., cells have an average life time of 2 days. The model accounts for a memory cell population of 5% of the peak population size by a reversal to memory of 1 to 2% of the activated cells per day during the death phase.
Animals↗
Arrhythmias in neurofibromatosis. A case report and review of the literature.
Patients with neurofibromatosis have a higher incidence of anatomic cardiac abnormalities. However, there is little data regarding incidence of arrhythmias in this population. It is known that these patients have a higher mortality than the normal population, and it is possible that some deaths may be due to preventable causes such as cardiac arrhythmias. We report a patient with neurofibromatosis who was treated for a refractory seizure disorder for 8 years. However, video/EEG monitoring demonstrated that the patient had recurrent syncopal seizures secondary to sinus node dysfunction. Complete resolution of symptoms occurred after a permanent pacemaker implantation. We believe this is the first reported case of sinus node dysfunction associated with neurofibromatosis.
Adult↗
Development and testing of an assessment tool for integrated learning.
OBJECTIVE: Development of integrated questions for undergraduate medical students and assessing students' capability to retain and apply basic concepts in an integrated way. METHOD: Multiple choice questions, attempting to probe understanding and application of different concepts, affiliated with different subjects and topics, were developed. As a pilot these were administered to the students of third year and final year at the end of their certifying examinations as a mock test. The following year these questions were introduced in the continuous assessments and subsequently the certifying examinations (in third year) as 33% of the whole examination. Difficult indices, item analysis and internal consistency (alpha) were calculated for all the questions. RESULTS: The difficulty indices of integrated questions indicated that students found the integrated questions difficult. CONCLUSION: There was a significant change of distribution in terms of scoring for the integrated questions. Students' power to integrate showed reliable improvement when tested in the certifying examinations.
Analysis of Variance↗
Parental [correction of Perinatal] consanguinity: a risk factor for developmental delay in Pakistani children.
OBJECTIVE: To investigate the association of parental consanguinity and delayed development in terms of gross motor, fine motor, speech and social aspects in their children. METHODS: One hundred and seventy seven children (age 15 days--72 months) were evaluated for their developmental status utilizing the Denver Developmental Screening Test (DDST). An unmatched case-control study design was used. Case group consisted of 94 children and control group 83 children. Odds ratios were calculated for parental consanguinity and delay in gross and fine motor, speech and social development in their children, for cases and controls, utilizing Binary Multiple Logistic Regression Analysis. Acquired delay was excluded through detailed birth history in both cases and control group respectively. RESULTS: Univariate analysis showed high significant Odds ratios for all areas of developmental delay (viz. gross and fine motor, speech and social development), between cases and controls (p < .001). At the multivariate analysis level however, our results showed no increased risk of parental consanguinity on delayed gross and fine motor, speech and social development in their children. CONCLUSION: Our results show no increased risk of parental consanguinity on delayed gross and fine motor, speech or social development (as measured by the DDST), in their children.
Analysis of Variance↗
Studies on Achras sapotal: part IV--chemistry and pharmacology of wood.
Phytochemical screening of the n-hexane fraction of the alcoholic extract of Achras sapotal has shown the presence of oleane and ursane types of triterpenoids. Pharmacology of the alcoholic extract was studied on Wister rats anaesthetized with recommended dose. The extract caused a fall in systolic, diastolic and mean arterial blood pressure (MABP) in a dose depended manner.
Journal Article↗
Evolution of the T cell repertoire during primary, memory, and recall responses to viral infection.
Many viral infections induce a broad repertoire of CD8(+) T cell responses that initiate recognition and elimination of infected cells by interaction of TCRs with viral peptides presented on infected cells by MHC class I proteins. Following clearance of the infection, >90% of activated CD8(+) T cells die, leaving behind a stable pool of memory CD8(+) T cells capable of responding to subsequent infections with enhanced kinetics. To probe the mechanisms involved in the generation of T cell memory, we compared primary, memory, and secondary challenge virus-specific T cell repertoires using a combination of costaining with MHC class I tetramers and a panel of anti-Vss Abs, as well as complementarity-determining region 3 length distribution analysis of TCR Vss transcripts from cells sorted according to tetramer binding. Following individual mice over time, we found identity between primary effector and memory TCR repertoires for each of three immunodominant epitopes from lymphocytic choriomeningitis virus. During secondary responses, we found quantitative changes in epitope-specific T cell hierarchies but little evidence for changes in Vss usage or complementarity-determining region 3 length distributions within epitope-specific populations. We conclude that 1) selection of memory T cell populations is stochastic and not determined by a distinct step of clonal selection necessary for survival from the acute responding population, and 2) maturation of the T cell repertoire during secondary lymphocytic choriomeningitis virus infection alters the relative magnitudes of epitope-specific responses but does not significantly modify the repertoire of T cells responding to a given epitope.
Animals↗
Cutting edge: naive T cells masquerading as memory cells.
This study shows that naive CD8 T cells can acquire characteristics of memory T cells in the absence of stimulation with specific Ag simply by the process of homeostatic proliferation under lymphopenic conditions. This Ag-independent T cell differentiation pathway did not result in up-regulation of early activation markers (CD69, CD25, CD71), but expression of several memory markers (CD44, CD122, Ly6C) increased progressively with successive divisions. These markers were then stably expressed, and these cells also became more responsive functionally to specific Ag. Thus, all "memory" phenotype T cells in an individual may not be true Ag-experienced cells and may include naive cells masquerading as memory cells. These findings are specially relevant in cases of disease or treatment-induced lymphopenia such as in HIV-infected individuals or transplant recipients. In addition, this study may have implications for autoimmunity because homeostatic proliferation of naive T cells requires interaction with self peptide plus MHC molecules.
Animals↗
Cutting edge: increased expression of Bcl-2 in antigen-specific memory CD8+ T cells.
Bcl-2 plays a critical role in regulating cell survival and apoptosis. We examined Bcl-2 expression in virus-specific CD8 T cells during the expansion, death, and memory phases of the T cell response following infection of mice with lymphocytic choriomeningitis virus (LCMV). Naive CD8 T cells expressed a basal level of Bcl-2 that was down-regulated in effector CD8 T cells just before the death phase. Bcl-2 levels remained low during the death phase but surviving memory CD8 T cells expressed higher levels of Bcl-2 than naive cells. These changes were shown to occur in LCMV TCR transgenic cells as well as virus-specific CD8 T cells in C57BL/6 and BALB/c mice identified by MHC class I tetramers. In all instances, memory CD8 T cells expressed higher levels of Bcl-2, suggesting that increased Bcl-2 expression plays a role in the long-term maintenance of memory CD8 T cells in vivo.
Animals↗
Differentiating between memory and effector CD8 T cells by altered expression of cell surface O-glycans.
Currently there are few reliable cell surface markers that can clearly discriminate effector from memory T cells. To determine if there are changes in O-glycosylation between these two cell types, we analyzed virus-specific CD8 T cells at various time points after lymphocytic choriomeningitis virus infection of mice. Antigen-specific CD8 T cells were identified using major histocompatibility complex class I tetramers, and glycosylation changes were monitored with a monoclonal antibody (1B11) that recognizes O-glycans on mucin-type glycoproteins. We observed a striking upregulation of a specific cell surface O-glycan epitope on virus-specific CD8 T cells during the effector phase of the primary cytotoxic T lymphocyte (CTL) response. This upregulation showed a strong correlation with the acquisition of effector function and was downregulated on memory CD8 T cells. Upon reinfection, there was again increased expression of this specific O-glycan epitope on secondary CTL effectors, followed once more by decreased expression on memory cells. Thus, this study identifies a new cell surface marker to distinguish between effector and memory CD8 T cells. This marker can be used to isolate pure populations of effector CTLs and also to determine the proportion of memory CD8 T cells that are recruited into the secondary response upon reencounter with antigen. This latter information will be of value in optimizing immunization strategies for boosting CD8 T cell responses.
Animals↗
Antiviral CD4 and CD8 T-cell memory: differences in the size of the response and activation requirements.
Following acute lymphocytic choriomeningitis virus (LCMV) infection, there is a potent antiviral CD8 T-cell response that eliminates the infection. This initial CD8 T-cell response is followed by a period of memory during which elevated numbers of virus-specific CD8 T cells remain in the mouse. CD4 T cells are also activated after LCMV infection, but relatively less is known about the magnitude and duration of the CD4 response. In this study, we used intracellular staining for interferon-gamma to measure both CD4 and CD8 responses in the same mice at the single cell level. After LCMV infection, there was an increase in the number of activated CD4 T cells and an associated increase in the number of virus-specific CD4 T cells. At the peak of this expansion phase, the frequency of virus-specific CD4 T cells was 1 in 20 (0.5-1.0 x 10(6) per spleen). Like the CD8 response, long-term CD4 memory could be found up to a year after the infection with frequencies of approximately 1 in 260 (0.5-1.5 x 10(5) per spleen). However, the magnitude of virus-specific CD8 T cells was greater than virus-specific CD4 T cells during all phases of the immune response (expansion, death, and memory). At day 8, there were 20- to 35-fold more virus-specific CD8 T cells than CD4 T cells. This initial difference in cell number lasted into the memory phase as there remained a ten- to 20-fold difference in the CD8 and CD4 responses. These results highlight the importance of the expansion phase in determining the size of the memory T-cell pool. In addition to the difference in the magnitude, the activation requirements of CD8 and CD4 T-cell responses were different: CD8 T responses were not affected by blockade of CD40-CD40 ligand interaction whereas CD4 responses were reduced 90%. So while there is long-term memory in both the CD8 and CD4 compartments, the rules regulating the activation of CD8 and CD4 T cells and the overall magnitude of the responses are different.
Animals↗
4-1BB costimulation is required for protective anti-viral immunity after peptide vaccination.
Peptide vaccination induces T cell activation and cytotoxic T cell development. In an effort to understand what factors can improve immune responses to peptide vaccination, the role of 4-1BB (CD137) costimulation was examined, since 4-1BB has been shown to promote T cell responses in other systems. 4-1BBL-deficient (-/-) and wild-type (+/+) mice were immunized with a lipidated lymphocytic choriomeningitis virus (LCMV) peptide NP396-404. Analysis of peptide-specific responses early after immunization by CTL assay, intracellular IFN-gamma staining, and IFN-gamma enzyme-linked immunospot assay (ELISPOT) indicated that CD8 T cell responses were reduced 3- to 10-fold in the absence of 4-1BB costimulation. Moreover, when agonistic anti-4-1BB Ab was given, CD8 T cell responses in 4-1BBL-/- mice were augmented to levels similar to those in 4-1BBL+/+ mice. Two months after immunization, 4-1BBL+/+ mice still had epitope-specific cells and were protected against viral challenge, demonstrating that peptide vaccination can induce long-term protection. In fact, 70% of CD8 T cells were specific for the immunizing peptide after viral challenge, demonstrating that strong, epitope-specific CD8 T cell responses are generated after peptide vaccination. In contrast, peptide-immunized 4-1BBL-/- mice had fewer epitope-specific cells and were impaired in their ability to resolve the infection. These results show that immunization with a single LCMV peptide provides long term protection against LCMV infection and point to costimulatory molecules such as 4-1BB as important components for generating protective immunity after vaccination.
Animals↗