shadow_tr

Comparative Pathology

photo: disease

The Division of Comparative Pathology conducts tissue-based studies of disease processes with the major focus on infectious diseases including AIDS, malaria and tuberculosis.

The Division consists of thirty-eight members including nine faculty, five postdoctoral fellows, twenty-two research technicians, and two administrative staff. Dr. Ronald S. Veazey, Professor of Pathology at Tulane Medical School, is Chairman of the Division.

The functions of the Division can be divided into three main areas:

  1. Research Programs
  2. Research Resources
  3. Education & Training Opportunities.

Research Programs

The research component of the Division is very active and involves collaborative and independent work in a number of areas focusing on mechanisms of disease and development of new animal models. The research activities of the Division can be divided into investigations into the pathogenesis, treatment and prevention of AIDS, the effects of malaria on the immune system in pregnancy and children, and the pathogenesis and immunology of tuberculosis infections.

Acquired Immune Deficiency Syndrome (AIDS)

More people die from AIDS each year than from any other infectious disease. Over 5 million people die from AIDS every year (about 14,000 per day) making this perhaps the greatest infectious disease threat to the human race. In the United States, AIDS is the second leading cause of death in young adults (18-40 years of age) and is second only to automobile accidents. Investigation of AIDS pathogenesis, prevention and treatment represent the largest research objective of the Division and encompass a number of projects examining 1) the macaque model of neuroAIDS, 2) AIDS and the mucosal immune system, 3) the development of microbicides to prevent HIV heterosexual transmission of AIDS, and 4) testing new therapies for AIDS.

Macaque model of neuroAIDS

Infection of rhesus macaques with SIV results in rapid neuroinvasion and neuropathologic abnormalities that are similar to those observed in HIV-infected humans. We have used this model to examine the role of chemokines and their receptors in neuroinvasion and the development of neuronal injury and neurologic disease. We previously demonstrated elevated expression of the chemokines MIP-1a, MIP-1b, and RANTES and the corresponding receptors CCR3, CCR5, and also CXCR4 in perivascular infiltrates in the brain. Of additional interest was the presence of CCR3, CCR5, and CXCR4 on a subpopulation of large hippocampal and neocortical pyramidal neurons and on glial cells in both normal and SIV-infected brain. The expression of known HIV/SIV coreceptors on neurons and astrocytes suggested a possible mechanism whereby HIV/SIV or the chemokines they induce could interact with these cells, disrupting their normal physiologic function and contributing to the neuropathogenesis of AIDS. To address this hypothesis, we have used immediately ex vivo and in vitro techniques to confirm the presence of all three of these chemokine receptors on a subpopulation of neurons and CCR5 and CXCR4 expression on the majority of astrocytes. These chemokine receptors are functional as demonstrated by increased intracellular calcium in response to the appropriate ligand. We have also used proton magnetic resonance spectroscopy (MRS) to evaluate the neuronal marker n-acetylaspartate (NAA) both in vivo and ex vivo. A 25% decrease in NAA was detected 14 days after infection coincident with peak viremia, neuroinvasion and increased numbers of perivascular macrophages. Decreases in NAA were correlated with decreases in synaptophysin and calbindin in adjacent sections of brain. A further 10% decrease in NAA levels was observed in animals infected for two years or more regardless of the presence of SIV-encephalitis (SIVE). These results indicate that neuronal injury occurs early after viral infection, is associated with neuroinvasion and progresses during the course of infection. The interaction of chemokines or viral envelope with these functional chemokine receptors on neurons and astrocytes suggests a physiologic mechanism whereby neuronal injury could occur.

AIDS and the mucosal immune system

The Division has several ongoing AIDS-related projects to examine the pathogenesis, prevention, and treatment of HIV infection. Much of this work focuses on the vaginal and intestinal mucosa as well as the mucosal immune system in general. Previously, we had shown that rapid and profound CD4+ T cell depletion occurs almost exclusively within the intestinal tract of simian immunodeficiency virus (SIV)-infected macaques within days of infection. In more recent work, we have shown that intestinal CD4+ T cells have much higher expression of CCR5 than T cells in peripheral blood or lymph nodes. Furthermore, the selectivity and extent of CD4+ T cell loss may depend upon these cells co-expressing CCR5 and having a "memory" phenotype. These seminal studies we originally performed in macaques were finally confirmed in HIV-infected humans in 2004 which has resulted in a heightened interest in studying the mucosal immune system and AIDS.

In addition, we have also demonstrated that CCR5 expression on CD4+ T cells may be fundamentally involved in the pathogenesis of AIDS and disease progression (or the lack thereof) by examining expression of these markers in sooty mangabeys (SM) and African green monkeys (AGM). Sooty mangabeys and AGM are the natural host of SIV, and despite persistent high viral loads, these animals rarely progress to AIDS. We have recently discovered that both sooty mangabeys and AGMs naturally have markedly lower percentages of CD4+CCR5+ T cells in their tissues, which could explain why these animals do not progress to AIDS. This finding could have significance for treatment and vaccine strategies in HIV patients.

Heterosexual transmission of AIDS: Development of microbicides to prevent transmission

The development of a microbicide that could be applied to the vagina and prevent the transmission of HIV-1 could save millions of lives. Unfortunately, compounds that destroy HIV-1 are also likely to damage mucosal tissues. Alternatively, fusion inhibitors that attach to viral or host cell receptors may provide a safe and effective mechanism to prevent HIV-1 infection. In 2003, we demonstrated that applying a compound to the vagina of monkeys that blocked the molecule responsible for viral attachment to the host CD4 molecule could completely prevent the vaginal transmission of SHIV (a virus having the HIV outer envelope). In 2004, we demonstrated that a CCR5 blocking agent (PSC-RANTES) could also completely prevent the vaginal transmission of SHIV when introduced as a topical application in the vagina. These studies were the first to demonstrate that CD4 or CCR5 fusion inhibitors could be part of an effective HIV preventative (microbicide). In more recent studies, we have demonstrated that a small molecule inhibitor of CCR5 can prevent vaginal SDHIV transmission. We are continuing to test this fusion inhibitor with the goal of producing a cheap and effective microbicide that could be distributed to places where the epidemic is rampant to slow the spread of HIV infection.

Testing new therapies for AIDS

Although remarkable progress has been made in anti-viral therapies in the last few years, no patient has been cured of infection, and increasingly, patients are showing resistance to anti-HIV drugs in use today. With the rapid and spreading emergence of multi-drug resistant strains of HIV, new classes of anti-HIV therapies are needed to combat HIV infections and for the prevention of AIDS. We are currently testing fusion inhibitors in SIV-infected rhesus macaques to determine whether they may affect viral loads and whether they may be useful as single or combinational therapies against SIV and SHIV-infected macaques. We have demonstrated that certain compounds have remarkable efficacy in reducing viral loads in SIV-infected macaques and are currently testing whether these changes correlate with reductions in chemokine receptor expression, and/or result in viral envelope mutations that may result in drug resistance. These compounds are being tested for efficacy, drug resistance and safety in nonhuman primates.

Malaria

The Division has developed a nonhuman primate model of malaria during pregnancy. Plasmodium coatneyi is used to infect rhesus monkeys with severe malaria during pregnancy and induces clinical features and placental pathology very similar to those caused by P. falciparum in pregnant women. The goal of these studies is to determine the etiology of the poor fetal outcome (abortion, low birth weight, early infant death, etc.) that occurs when pregnancy is complicated by malaria. The aims include the role that parity (number of prior pregnancies) and prior immunity to malaria plays, as well as the direct and indirect effects of malaria on the maternal and fetal immune system. Much of this work involves investigating the combination of immune responses associated with successful pregnancy, the effective defenses against malaria, and the effect that these two diametrically opposed responses have on the placenta and placental function. This work has led to collaborative studies of human placental pathology induced by P. falciparum and P. vivax in pregnant women at the Shoklo Malaria Research Unit in Mae Sot, Thailand.

Tuberculosis

Work on tuberculosis is focused on development of new vaccines and diagnostics. The vaccine work is a collaborative effort with investigators from Duke University, Albert Einstein College of Medicine, and Harvard University. In these studies, we are using gene deletion mutants of Mycobacterium tuberculosis developed by our collaborators and designated 6020 and 6030. These two deletion mutants are extremely safe in rodents and have been shown to be more effective at preventing tuberculosis (TB) than BCG. We have shown that these mutants are also safe in cynomolgus macaques, and we are in the middle of a protection study comparing 6020 and 6030 with BCG.

We are also working on testing and developing improved diagnostic tests for tuberculosis. a rapid test has been developed that is an easy-to-perform, single-use diagnostic test for visual detection of antibodies to the mycobacterium that cause tuberculosis. This format provides a test that is simple (requires neither electricity nor expensive equipment for test execution or reading, nor skilled personnel for test interpretation), rapid (turn around time less than 15 minutes), safe (minimizes handling of potentially infected specimens), non-invasive (requires 30 ml of serum), stable (can keep at least 18 months without refrigeration) and highly reproducible. We are currently testing the reliability of this kit in normal non-infected monkeys, false-positive skin test animals, and monkeys experimentally infected with tuberculosis to prove that it is specific, safe, and reliable for testing humans for the presence of the tuberculosis causing mycobacteria.

The TNPRC is a division of Tulane University (985) 871-6201 tnprc@tulane.edu