Biomedical subjects

R B Markham

Publications and source records attributed to R B Markham.

At least 19 recordsLinked to original sources

PubMed2003

Genetic influence of CXCR6 chemokine receptor alleles on PCP-mediated AIDS progression among African Americans.

CXCR6 is a chemokine receptor and the primary coreceptor in SIV infection. A single nucleotide polymorphism 1469G-->A, results in a nonconservative change in codon 3 (CXCR6-E3K) of the N-terminus of the coreceptor. To investigate the relation between the chemokine receptor CXCR6 genotype and progression to Pneumocystis carinii pneumonia (PCP) and from PCP to death, we clinically assessed and genotyped 805 individuals from an African-American injection drug-using cohort in Baltimore, MD, USA, for this CXCR6-E3K polymorphism. The allele frequency of CXCR6-3K was high (44%) in African Americans and rare in European Americans (f<1%). Although time to AIDS and PCP was similar for all CXCR6 genotypes, the median survival time from PCP to death for the CXCR6-3E/E and CXCR6-3E/K genotype was 1.5 years compared to 3.1 years for the CXCR6-K/K genotype. Individuals homozygous or heterozygous for the CXCR6-3E allele were 5.6 times more likely to die a PCP-mediated AIDS-related death than were individuals homozygous for CXCR6-3K. This study shows an association between CXCR6 genotype and progression from PCP to death among African-Americans with HIV. We suggest that CXCR6 may play a role in late-stage HIV-1 infection and may alter the progression to death after initial infection with PCP.

Acquired Immunodeficiency Syndrome↗

PubMed2000

Differences among HIV-1 variants in their ability to elicit secretion of TNF-alpha.

HIV-1 infection of human PBMC has been shown to elicit secretion of several different cytokines. TNF-alpha secretion induced by this virus has been of particular interest because it has been associated with the development of HIV-1 dementia and because TNF-alpha increases viral replication by enhancing NF-kappaB interaction with the viral promoter, the HIV-1 long terminal repeat. Thus, an autocrine pathway is potentially created in which HIV-1 stimulates its own replication. Conflicting reports exist, however, on the ability of HIV-1 to induce TNF-alpha secretion in vitro or in vivo. Using experimental protocols that controlled for potential bacterial endotoxin-induced TNF-alpha secretion, the current study demonstrates significant differences in TNF-alpha-eliciting properties among primary and laboratory obtained HIV-1. The relative TNF-alpha-inducing ability of different variants is conserved when tested using PBMC from different individuals. Elicitation of TNF-alpha secretion was not blocked by exposure of cells to zidovudine, indicating that viral integration was not required to induce secretion. Rather, the interaction between the virus and cell surface is critical for TNF-alpha induction, as Abs against CD4 or CCR5 blocked the induction of TNF-alpha synthesis by PBMC when added before virus exposure. Furthermore, the ability to induce TNF-alpha secretion mapped to a region of the HIV-1 env gene that includes the third hypervariable domain. Differences in the ability of different HIV-1 variants to elicit TNF-alpha may account for individual differences in HIV-1 disease course.

Antigenic Variation↗

PubMed1999

The effect of drug-injection behavior on genetic evolution of HIV-1.

The effect of injection-drug use on human immunodeficiency virus type 1 (HIV-1) env genetic evolution was examined in 15 seroconverting injection-drug users followed up for 4 years. After adjustment for non-drug-related independent variables significantly associated with genetic diversity (time since seroconversion and progressor status), injection frequency was positively and highly significantly associated with HIV-1 env genetic diversity (P=.003). The mutation rate in those who had injected at least once a day during the previous 6 months was estimated to be 62% greater than the rate in those who had not injected at all. If the positive effect of drug-injection frequency on env genetic diversity extends to the HIV-1 pol gene, the risk of emergence of resistance to antiretroviral drugs may be enhanced by increased drug-injection frequency, especially under the selection pressure of antiretroviral therapy.

Adult↗

PubMed1999

A perspective on cellular immunity in the elderly.

The increased incidence of infection and malignancy in elderly individuals has prompted many studies that demonstrate that the aging immune system is impaired. Most of these studies have focused on the impairment of acquired immunity provided by lymphocytes. While defects in acquired humoral and T-cell-mediated immunity may exist, increased susceptibility to infection may result from defects in the constitutive functioning of macrophages and granulocytes. Recognition of the potential importance of defects in constitutive immunity in the elderly may provide new opportunities for therapeutic and prophylactic intervention in this population.

Aged↗

PubMed1998

Sex differences in HIV-1 viral load and progression to AIDS.

BACKGROUND: Plasma HIV-1 RNA measurements are used for initiation of antiretroviral treatments. Whether the viral-load association with prognosis is similar in women and men is unknown. METHODS: We studied 812 specimens from 650 injection-drug users (IDUs) participating in a continuous observational study of patients based in a community clinic. HIV-1 load was measured by branched-chain DNA on samples from 527 IDUs from the baseline visit, and by reverse-transcriptase PCR and quantitative microculture on samples from 285 IDUs at a follow-up visit 3 years later. FNDINGS: Women had lower median viral-load measurements than men by branched-chain DNA (3365 vs 8907 copies/mL; p=0.001), reverse-transcriptase PCR (45416 vs 93130 copies/mL; p=0.02), and quantitative microculture (5 vs 8 infectious units per million peripheral blood mononuclear cells; p=0.015). This association remained even after adjustment for CD4 cell count, race, and drug use within the previous 6 months. Time to AIDS was statistically similar for men and women in a univariate proportional-hazards model and in a model adjusting for CD4 cell count. Proportional-hazards models showed that women with the same viral load as men had a 1.6-fold higher risk of AIDS (95% CI 1.10-2.32); or, equivalently, that women with half the viral load of men had a similar time to AIDS as men. INTERPRETATION: Although a biological mechanism remains unclear, these data suggest that current recommendations for HIV-1 viral-load thresholds to initiate antiretroviral therapy should be revised downwards for women.

Acquired Immunodeficiency Syndrome↗

PubMed1998

Patterns of HIV-1 evolution in individuals with differing rates of CD4 T cell decline.

Evolution of HIV-1 env sequences was studied in 15 seroconverting injection drug users selected for differences in the extent of CD4 T cell decline. The rates of increase of either sequence diversity at a given visit or divergence from the first seropositive visit were both higher in progressors than in nonprogressors. Viral evolution in individuals with rapid or moderate disease progression showed selection favoring nonsynonymous mutations, while nonprogressors with low viral loads selected against the nonsynonymous mutations that might have resulted in viruses with higher levels of replication. For 10 of the 15 subjects no single variant predominated over time. Evolution away from a dominant variant was followed frequently at a later time point by return to dominance of strains closely related to that variant. The observed evolutionary pattern is consistent with either selection against only the predominant virus or independent evolution occurring in different environments within the host. Differences in the level to which CD4 T cells fall in a given time period reflect not only quantitative differences in accumulation of mutations, but differences in the types of mutations that provide the best adaptation to the host environment.

Base Sequence↗

PubMed1998

Infection with dual-tropic human immunodeficiency virus type 1 variants associated with rapid total T cell decline and disease progression in injection drug users.

The characteristics of sequential human immunodeficiency virus type 1 (HIV-1) isolates from 12 seroconverters among injection drug users selected for either rapid or slow disease progression were evaluated. All 6 patients who developed AIDS within 5 years were initially infected with syncytium-inducing (SI) variants or showed a transition from non-SI-inducing (NSI) to SI variants. Detection of SI variants was associated with rapid decline of both CD8+ and CD4+ T cells. In contrast, the 6 slow progressors carried only NSI variants and maintained stable or increasing CD8+ T cell levels. The SI variants that were associated with initial infection were dual tropic, with efficient replication in primary macrophages and T cell lines. These results suggest that the ability to replicate in macrophages, rather than the SI or NSI phenotype per se, may be an important determinant of HIV-1 transmission and that dual-tropic viruses, when transmitted, may be associated with rapid progression to AIDS.

Adult↗

PubMed1998

Potential relationships between the presence of HIV, macrophages, and astrogliosis in SCID mice with HIV encephalitis.

The pathogenesis of HIV encephalitis (HIVE) has not been determined although increased numbers of mononuclear phagocytes (macrophages and microglia), some of which are HIV-infected, and reactive astrogliosis are important pathological findings in this condition. For this experiment, fifty-one SCID mice were inoculated intracerebrally either with human cells and HIV-1, human cells only or HIV only and then sacrificed at various time points. HIV gag mRNA was detected by reverse transcriptase polymerase chain reaction (PCR) distant from the site of inoculation in 73% of mouse brains inoculated with HIV and human cells attesting to the pervasiveness of HIV infection in SCID brain. HIV mRNA was detected as long as 91 days after inoculation of human cells and virus and the presence of HIV gag, nef, and tat/rev mRNA in HIV-infected SCID brains indicates ongoing HIV mRNA synthesis. Brain tissue sections were immunostained for HIV, human macrophages, and astrocytes from a subset of mice (n = 29) from the above groups and qualitatively assessed. PCR data for HIV mRNA was correlated with staining results and these data suggested that the greatest astrogliosis was present in mice inoculated with HIV and human cells, consistent with previously reported data. The data further suggest that astrogliosis is greater when HIV is detected. Taken together the data are consistent with a synergistic effect between macrophages and HIV in the development of astrogliosis.

AIDS Dementia Complex↗

PubMed1996

Conditional reduction of human immunodeficiency virus type 1 replication by a gain-of-herpes simplex virus 1 thymidine kinase function.

The development of an effective vaccine for human immunodeficiency virus type 1 (HIV-1) would be a major advance toward controlling the AIDS pandemic. Several disparate strategies for a safe and effective HIV vaccine have been proposed. Recent data suggest that loss-of-function live-attenuated virus could be a safe lentivirus vaccine. Here, we propose a gain-of-function approach that can complement loss-of-function in enhancing the safety profile of a live-attenuated virus. We describe an example in which ganciclovir (GCV) was used to treat effectively nef(-)HIV-1 engineered to express herpes simplex virus (HSV-1) thymidine kinase (TK). This treatment was found to be highly efficient in controlling HIV-1 spread in tissue culture and in a small animal (hu-PBL-SCID) model. We demonstrate that one distinct advantage of GCV-HSV-TK treatment is the elimination of integrated proviruses, a goal not easily achieved with other antiretrovirals.

AIDS Vaccines↗

PubMed1996

Selective transmission of human immunodeficiency virus type 1 variants to SCID mice reconstituted with human peripheral blood monoclonal cells.

The relative infectiousness of laboratory and primary human immunodeficiency virus type 1 (HIV-1) variants was evaluated in in vitro cell cultures of peripheral blood mononuclear cells or MT-2 cells and in Hu-PBL-SCID mice. HIV(MN) and syncytium-inducing primary isolates were preferentially transmitted to cells in tissue culture. HIV(Ba-L) and non-syncytium-inducing (NSI) primary isolates were more infectious in Hu-PBL-SCID mice. Phylogenetic analysis of env sequences derived from the primary isolates, from the cell cultures, and from five Hu-PBL-SCID mice was performed by using methods designed for resolving differences among closely related sequence pairs. This analysis demonstrated preferential transmission of an evolutionarily related subset of NSI variants to Hu-PBL-SCID mice. The pattern of selective transmission of a restricted range of NSI variants that is observed in the clinical setting is maintained in Hu-PBL-SCID mice and not in tissue culture systems. The Hu-PBL-SCID mouse model system, when used with appropriate phylogenetic analysis methodologies, will be useful for identifying and characterizing the more infectious HIV-1 variants that should be targeted for vaccine development.

Amino Acid Sequence↗

PubMed1995

Human immunodeficiency virus type 1 env and p17gag sequence variation in polymerase chain reaction-positive, seronegative injection drug users.

Variation in gene sequences from human immunodeficiency virus type 1 (HIV-1) p17gag and the third hypervariable region (V3 loop) of env was examined in a cross-sectional study of single specimens from 4 HIV-1 polymerase chain reaction-positive, seronegative injection drug users. As observed in sexually transmitted disease, clones of HIV-1 genes isolated from an individual were remarkably homogeneous, with amino acid variation in the envelope region of 0.3%-0.9% and in p17gag of 0.0%-0.7%. Intersubject variation was much greater (at the amino acid level, 15% for the envelope and 4.3% for p17gag), with conservation in the envelope only of regions at the base of the V3 loop. Since at least some subjects likely acquired infection intravenously, the ability of virus to survive in seminal fluid or on mucosal surfaces cannot explain the observed homogeneity, which may depend on direct interactions between the virus and the infected cell.

Amino Acid Sequence↗

PubMed1995

Clinically practical seminested PCR for Burkholderia pseudomallei quantitated by enzyme immunoassay with and without solution hybridization.

Diagnosis of melioidosis, an infectious disease caused by Burkholderia pseudomallei (formerly Pseudomonas pseudomallei), is made initially by antibody testing, which is not always sensitive or specific. We have developed two seminested PCR protocols combined with enzyme immunoassay (EIA) to detect the conserved ribosomal regulatory region of B. pseudomallei. Both PCRs used one biotinylated primer for capturing PCR products on EIA plates. One system, termed solution hybridization EIA (SHEIA), hybridized PCR products with a digoxigenin-labeled probe in solution. Another system, termed primer-labeled EIA (PLEIA), used a digoxigenin-labeled nested primer to generate products that were directly detected without hybridization. To prevent amplicon contamination, pre-PCR uracil DNA glycosylase treatment or post-PCR UV irradiation was incorporated into each system. By a rapid method of blood sample preparation for PCR, these systems had sensitivities of 75 bacteria per ml for SHEIA and 300 bacteria per ml for PLEIA. No nonspecific amplification of other bacterial DNAs was detected. This seminested PCR coupled with SHEIA or PLEIA fulfills all the requirements for a diagnostic test to be used in developing countries where B. pseudomallei is endemic.

Bacteremia↗

PubMed1994

Maternal IgG1 and IgA antibody to V3 loop consensus sequence and maternal-infant HIV-1 transmission.

Maternal-infant transmission of HIV-1 occurs in 13-40% of pregnancies. Studies on transmission of maternal immunity to HIV antigens have used antigens from viruses not representative of clinical isolates and have been conflicting. Using a consensus peptide sequence based on HIV isolates found in Haiti, we found that Haitian mothers who transmitted infection to their offspring had significantly higher mean concentrations of IgG1 antibodies to the V3 loop of the primary neutralising domain of the viral envelope (gp 160) than non-transmitters (p = 0.02). Concentrations of IgA antibody to this domain were similar in transmitters and non-transmitters.

Amino Acid Sequence↗

PubMed1993

A model of human immunodeficiency virus encephalitis in scid mice.

Human immunodeficiency virus (HIV)-associated dementia complex is a common and devastating manifestation of the late phases of HIV infection. The pathogenesis of dementia complex is poorly understood and effective treatments have not been developed, in part because of the lack of an appropriate animal model. Mice with severe combined immunodeficiency (scid mice), which accept xenografts without rejection, were intracerebrally inoculated with human peripheral blood mononuclear cells and HIV. One to 4 weeks after inoculation, the brains of these mice contained human macrophages (some of which were HIV p24 antigen positive), occasional multinucleated cells, and striking gliosis by immunocytochemical staining. Human macrophages also were frequently positive for tumor necrosis factor type alpha and occasionally for interleukin 1 and VLA-4. Cultures of these brains for HIV were positive. Generally, human macrophages were not present in the brains of control mice, nor was significant gliosis, and HIV was not recovered from mice that received HIV only intracerebrally. Pathologically, this model of HIV encephalitis in scid mice resembles HIV encephalitis in humans and the data suggest that the activation of macrophages by infection with HIV results in their accumulation and persistence in brain and in the development of gliosis. This model of HIV encephalitis should provide insights into the pathogenesis and treatment of this disorder.

AIDS Dementia Complex↗

PubMed1993

Biologic effects after a single dose of poly(I):poly(C12U) in healthy volunteers.

Poly(I):poly(C12U) (mismatched double-stranded RNA; atvogen), an interferon inducer, is active against human immunodeficiency virus in vitro. To determine the extent and duration of the biologic effects of poly(I):poly(C12U), we administered a single dose of the drug to healthy volunteers in a randomized, double-blind, placebo-controlled 2-week crossover study. We analyzed blood for alpha and gamma interferons, neopterin, 2',5'-oligoadenylate synthetase, lymphocyte surface markers, lymphocyte proliferation after exposure to soluble antigens and mitogens, and natural killer cell activity. Minimal biologic effects were observed after administration of a single 200-mg dose to four volunteers; therefore, the dose was increased to 600 mg in 10 subjects. Only neopterin levels and symptoms were greater after administration of 600 mg of poly(I):poly(C12U) than after administration of placebo (Wilcoxon signed rank sum test, P = 0.06). A definite response in 2',5'-oligoadenylate synthetase activity, however, was seen in a few subjects. Neither alpha nor gamma interferon was detectable in serum after poly(I):poly(C12U) dosing. The neopterin changes after administration of poly(I):poly(C12U) were similar at both poly(I):poly(C12U) dose levels, with an early decrease at 6 h, a peak at 1 day, and a gradual decrease toward the baseline over the following 3 days. A mild flu-like syndrome occurred in one-half of the subjects following administration of poly(I):poly(C12U) and in only one subject following administration of placebo. This syndrome resolved within 16 h after poly(I):poly(C12U) dosing. We conclude that poly(I):poly(C12U) does not induce measurable levels of interferon and causes only minimal biologic or toxic effects among those parameters measured after administration of a single dose in the 200- to 600-mg dose range in health volunteers.

2',5'-Oligoadenylate Synthetase↗

PubMed1993

Immune complexes from immunized mice and infected cystic fibrosis patients mediate murine and human T cell killing of hybridomas producing protective, opsonic antibody to Pseudomonas aeruginosa.

We examined the basis for the absence in cystic fibrosis (CF) patients of opsonic antibodies to the mucoid exopolysaccharide (MEP) antigen surrounding Pseudomonas aeruginosa that infect these patients. Opsonic antibodies to MEP are found in sera of the minority of CF patients that remain noncolonized into the second to fourth decades of life and protect rodents from chronic P. aeruginosa endobronchial infections. High titers of nonopsonic antibodies to MEP are found in P. aeruginosa-infected CF patients. Immunization of mice with doses of MEP that provoke only nonopsonic antibodies elicited CD3+, CD8+, T cell receptor alpha beta receptor+, major histocompatibility complex-unrestricted cytotoxic lymphocytes specific for hybridoma cells producing opsonic but not nonopsonic antibodies. Cytotoxicity was dependent on immune complexes on the surface of the T cells. Normal murine T cells could be activated by concanavalin A and sensitized with immune complexes for cytotoxic killing of hybridoma targets. CF patients infected with P. aeruginosa had serum immune complexes that sensitized concanavalin A-activated human T cells to kill murine hybridoma cells producing opsonic but not nonopsonic antibody. These results could explain the absence in infected CF patients of MEP-specific opsonins, an occurrence that accompanies the persistence of this infectious state.

Animals↗

PubMed1992

Mouse model for exoerythrocytic stages of Plasmodium falciparum malaria parasite.

Research on the exoerythrocytic (EE) stages of human malaria parasites has been hindered because of the lack of an easily available suitable animal model. We report here an approach to produce mature EE-stage Plasmodium falciparum parasites by using severe combined immunodeficient (scid) mice with transplanted human hepatocytes. Transplantation of human hepatocytes into scid mice (scid hu-hep), their subsequent intravenous infection with P. falciparum sporozoites, and the development of mature liver-stage merozoites was achieved. Immunofluorescent staining of scid hu-hep kidney tissue sections demonstrated the presence of circumsporozoite protein (early during infection), merozoite surface antigen 1, and liver schizont antigen 1. The scid hu-hep model can serve as a source of human malaria liver-stage parasites, decreasing the need for nonhuman primates. Use of this model will facilitate characterization of EE-stage antigens and the assessment of stage-specific chemotherapeutic agents and candidate vaccines.

Animals↗

PubMed1992

Effect of donor and recipient immunization protocols on primary and secondary human antibody responses in SCID mice reconstituted with human peripheral blood mononuclear cells.

We have examined the ability of mice with severe combined immunodeficiency (SCID mice) reconstituted with human peripheral blood mononuclear cells (PBMC) to generate human antibody responses after specific immunization. SCID mice reconstituted with cells from a keyhole limpet hemocyanin (KLH)-naive donor are unable to generate specific human antibody responses after immunization with that antigen. After KLH immunization, SCID mouse recipients of human PBMC from a KLH-immune subject develop specific human antibody levels exceeding those of the donor. Human antitetanus antibody titers in reconstituted, immunized mice are also equivalent to those of the donor, provided that the mice are immunized within days of human cell transplantation. The ability of reconstituted mice to generate high titers of specific human antibody is lost within 35 days of human cell reconstitution, even though titers of total human immunoglobulin (Ig) are preserved. SCID mice reconstituted with tetanus-immune donor cells fail to generate IgA responses after booster immunization, and IgM responses are low or nonexistent. These data indicate that early exposure of the adoptive recipients of human cells to antigen is required to transfer specific human humoral responses. These findings are also consistent with a requirement for persistence of antigen for the maintenance of B-cell memory. The ability to achieve specific human antibody levels equivalent to those obtained with humans indicates that reconstituted mice may be useful for the evaluation of human antibody-mediated mechanisms of resistance to infection. The data indicate, however, that cells from immunized donors will have to be used for such studies.

Animals↗