Understanding and overcoming the barriers to T cell-mediated immunity against tuberculosis

Despite the overwhelming success of immunization in reducing, and even eliminating, the global threats posed by a wide spectrum of infectious diseases, attempts to do the same for tuberculosis (TB) have failed to date. While most effective vaccines act by eliciting neutralizing antibodies, T cells are the primary mediators of adaptive immunity against TB. Unfortunately, the onset of the T cell response after aerosol infection with Mycobacterium tuberculosis (Mtb), the bacterium that causes TB, is exceedingly slow, and systemically administered vaccines only modestly accelerate the recruitment of effector T cells to the lungs. This delay seems to be orchestrated by Mtb itself to prolong the period of unrestricted bacterial replication in the lung that characterizes the innate phase of the response. When T cells finally arrive at the site of infection, multiple layers of regulation have been established that limit the ability of T cells to control or eradicate Mtb. From this understanding, emerges a strategy for achieving immunity. Lung resident memory T cells may recognize Mtb-infected cells shortly after infection and confer protection before regulatory networks are allowed to develop. Early studies using vaccines that elicit lung resident T cells by targeting the lung mucosa have been promising, but many questions remain. Due to the fundamental nature of these questions, and the need to understand and manipulate the early events in the lung after aerosol infection, only coordinated approaches that utilize tractable animal models to inform human TB vaccine trials will move the field toward its goal.     

Design of engineered vaccines for systemic and mucosal immunity to HIV

To design vaccines for viruses such as HIV that do not elicit sufficient protective immunity, we first constructed cluster vaccines containing T helper, CTL and neutralizing antibody epitopes. For second generation vaccines, we increased responses by enhancing binding to Major Histocompatibility molecules or by incorporating cytokines. We found that high avidity CTL induce better viral clearance. We also induced anti-HIV mucosal T cell immunity by intrarectal administration. Such approaches may improve classic attenuated or killed pathogen vaccines.     

Western medicine and traditional healers: partners in the fight against HIV/AIDS

Prevention and control programs for HIV/AIDS have had limited success, especially in sub-Saharan Africa. Not surprising, most residents see traditional healers as their only option to meet their healthcare needs. Some patients refuse surgery or other medical treatment unless their traditional healer sanctions the treatment first. Formally trained doctors have finally begun to consider traditional healers as potential allies in the battle to prevent the spread of HIV/AIDS by recognizing that the longstanding trust and credibility of these healers in the black communities can facilitate change in sexual behavior. Innovative and effective approaches, including utilization of traditional healers, can play a vital role in Africa's AIDS prevention and control programs.     

Intergrating health research with socio-cultural systems in the fight against HIV/AIDS

The rapid spread of AIDS in Africa has brought into focus the need to integrate medical science with socio-cultural beliefs and practices. The scientific knowledge on HIV, immune systems and drugs is well established. However, the drugs which are in use in the developed countries are too expensive for the great majority of the persons with HIV/AIDS in Africa. On the other hand, Africa is rich in socio-cultural traditions which have served their respective communities well. However, because of poverty and ignorance, many of the socio-cultural systems are helping in HIV/AIDS to spread increasingly fast. This therefore means that the most important weapon that Africa has for fighting HIV/AIDS is education through our socio-cultural systems. In this connection, for example, it is necessary to make the people understand that malnutrition will help the HIV to destroy the immune systems faster than it would do in a well-nourished person. This means therefore that the people need to be educated on the types of foods they must eat in order to get the necessary vitamins, proteins and calories. This is turn has implications on agricultural practices. It is also vital to make the people understand that other diseases do help HIV in suppressing immunity and that they should seek medical help as soon as they feel unwell. HIV/AIDS is a very expensive public health crisis. Families and health services are finding it difficult to meet all the needs of persons with AIDS. It is because of this that the rich African tradition of mutual social responsibility can play a major role in ameliorating the suffering and sharing the responsibility. A very major component of mutual social responsibility is co-operation and co-operative education among members of the community. Since the young persons constitute the most affected population , an educational system based on socio-cultural tradition of mutual social responsibility will help the young persons to acquire socially acceptable values and ethics which they need for survival. What has been said about HIV/AIDS is applicable to all health problems such as malaria and mother to child health (MCM). Health research and publications are important in making health policies precise and relevant. The application of those precise policies in solving health problems in Africa will in turn be more cost-effective and cost-beneficial if they are integrated with the socio-cultural systems.     

The importance of mucosal immunity in defense against epithelial cancers

Many cancers arise in epithelial mucosa. These mucosal surfaces are characterized by the induction of divergent immune responses, as they are both the main portal of entry for pathogens and a large niche of commensal bacteria and tolerized antigens. In addition, mucosa located in different anatomical sites harbor distinct typical features. Exploiting the different requirements for inducing an effective immune response at mucosal sites might help to define new immunotherapeutic approaches against epithelial cancers, at least in the case of differentiated tumors that have retained their mucosal characteristics.     

Blastogenic lymphocyte response as indicator of cell-mediated immunity in humans vaccinated with live and inactivated influenza vaccines

The level and dynamics of lymphocyte blastogenesis in response to phytohaemagglutinin (PHA) and to specific influenza virus antigen were studied in 3 groups of humans, vaccinated with live or inactivated whole virion influenza vaccines (H3N2 type) and placebo (control group). Both live and inactivated influenza vaccines did not change significantly the functional activity of T lymphocytes as determined by the mean values of stimulation index (SI). The analysis of individual values of PHA-dependent blastogenic response, however, revealed a decrease in SI as compared with its prevaccination level in 33.3 +/- 11.4% of the vaccinees given the live influenza vaccine.     

Role of Janus kinase 3 in mast cell-mediated innate immunity against gram-negative bacteria

Mast cells play a pivotal role in innate host immune response to gram-negative bacteria. We report that Janus kinase 3 plays a role in mast cell-mediated bacterial clearance and neutrophil recruitment by regulating the release of tumor necrosis factor from mast cells. The role of JAK3 in mast cell-facilitated neutrophil recruitment and bacterial clearance was investigated by comparing the neutrophil influxes and bacterial clearance in mast cell-deficient W/W(v) mice reconstituted with JAK3(+/+) or JAK(-/-) mast cells. The neutrophil influx, bacterial clearance, and survival outcome in W/W(v) mice reconstituted with JAK3(+/+) mast cells was better than in W/W(v) mice reconstituted with JAK3(-/-) mast cells. These findings provide evidence that JAK3 is a key regulator of mast cell-mediated innate immunity against gram-negative bacteria.     

Effect of the new immunostimulator HAB 439 on cell-mediated immunity against intracellular bacteria.

The isoxazoline derivative HAB 439 was tested for its enzyme inhibiting potency and was found to be an inhibitor of aminopeptidase B (IC50 = 22.5 micrograms/ml). In further immunopharmacological experiments its efficacy to stimulate cell-mediated immunity was evaluated. HAB 439 was shown to stimulate DTH-reaction against Salmonella typhimurium and Listeria monocytogenes. HAB 439 protected animals against infection by reducing the bacterial load in livers and spleens and by decreasing the mortality rate. Treatment with the antibiotic ampicillin induced a decreased DTH-reaction in mice which was demonstrated to be due to a reduction of the antigen to be presented to the immune system and not to immune suppression. HAB 439 restored the impaired immune response to S. typhimurium and L. monocytogenes in a dose-dependent way. Restoration of DTH was shown to lead to an improvement of protection in ampicillin-treated mice which were challenged with the intracellular bacteria.     

Alteration of cell-mediated immunity to Listeria monocytogenes in protein-malnourished mice treated with thymosin fraction V.

Cell-mediated immune reactivity, measured by lymphocyte responsiveness to phytohemagglutinin, was higher in both young or aged mice fed a 4% casein diet compared with age-matched controls. Treatment in vivo with bovine thymosin fraction V decreased the responsiveness to phytohemagglutinin of lymphocytes from mice fed either the control or moderately protein-deficient diets when compared with mice treated in vivo with saline. Resistance against Listeria monocytogenes, known to be a cell-mediated immune function, was impaired in young and aged mice which were fed the low-protein diet. Treatment with thymosin was able to significantly improve the cell-mediated immune resistance to L. monocytogenes of moderately protein-malnourished mice. Thymosin treatment impaired the resistance to L. monocytogenes of young or aged mice fed the control diet. The splenic natural killer cell cytotoxicity of protein-malnourished mice was impaired compared with that of mice fed the control diet. Treatment with thymosin did not restore the natural killer cell cytotoxic activity in protein-malnourished mice, but did enhance that activity in control mice.     

Hypersensitivity in the small intestinal mucosa. V. Induction of cell-mediated immunity to a dietary antigen.

Feeding of a protein antigen to adult mice results in reduced humoral and cell-mediated immune (CMI) responses when that antigen is subsequently presented, and also causes activation of suppressor cells in the gut-associated lymphoid tissues (GALT). We have attempted to abrogate this tolerance to fed antigen by pretreating mice with 100 mg/kg cyclophosphamide before oral immunization and challenge with ovalbumin. Cyclophosphamide-pretreated mice did not develop serum haemagglutinating antibodies, nor systemic CMI (as assessed by skin testing) after ovalbumin feeding. However, evidence that CMI had been induced in the GALT was provided by the significant inhibition of migration and mesenteric lymph node cells from cyclophosphamide-pretreated animals, but not from other control groups. in the presence of ovalbumin. Our previous work on CMI reactions in the small intestine has shown that the cell production rate in the crypts of Lieberkuhn and the intraepithelial lymphocyte count are reliable although indirect measures of mucosal CMI. Cyclophosphamide-pretreated, ovalbumin-immunized animals, which had been fed 0 . 1 mg ovalbumin daily for 10 days before killing, had increased crypt cell mitoses, and increased intraepithelial lymphocyte counts, indicating the presence of mucosal CMI response to ovalbumin. Mechanisms whereby cyclophosphamide pretreatment leads to abrogation of tolerance and induction of mucosal CMI are discussed.     

Cytokine and chemokine expression in the central nervous system associated with protective cell-mediated immunity against Cryptococcus neoformans.

Cryptococcus neoformans is a yeast that causes cryptococcosis, a life-threatening disease that develops following inhalation and dissemination of the organisms. C. neoformans has a predilection for the central nervous system (CNS) and mortality is most frequently associated with meningoencephalitis. Susceptibility to cryptococcosis is increased in patients with deficiencies in cell-mediated immunity (CMI). Because cryptococcal CNS infections are associated with mortality and diagnosis of cryptococcosis is often not made until after dissemination to the CNS, a better understanding of host defense mechanisms against C. neoformans in the CNS is needed to design improved therapies for immunocompromised individuals suffering from cryptococcosis. Using a mouse model, we previously described a protective cell-mediated immune response induced in the periphery that limited the growth of C. neoformans in the CNS. In the current investigation, we examined cytokine and chemokine expression in the CNS to identify factors important in achieving protective immunity. We observed increased expression of IL-1beta, TNF-alpha, IFN-gamma, MCP-1, RANTES, and IP-10 in C. neoformans-infected brains of immune mice compared to control mice suggesting that these cytokines and chemokines are associated with the protective immune response. Furthermore, the Th1-type cytokines TNF-alpha and IFN-gamma, but not the Th2 cytokines IL-4 and IL-5, were secreted at significantly higher levels in C. neoformans-infected brains of immune mice compared to control mice. Our results demonstrate that cytokines and chemokines associated with CMI are produced following infection in the CNS of immunized mice, and the expression of these factors correlates with protection against C. neoformans in the CNS.     

Construction of DNA vaccines and their induced protective immunity against experimental Eimeria tenella infection

In an attempt to construct a DNA vaccine against chicken coccidiosis, the TA4 gene of Eimeria tenella strain BJ was ligated to the mammalian expression vector pcDNA3.1/Zeo(+) to give pcDNA3.1-TA4 (pcDT). Then, Et1A (E. tenella refractile body gene) was ligated to it, upstream, aiming to be expressed in fusion with TA4, giving pcDNA3.1-Et1A-TA4 (pcDET). The constructed DNA vaccines were given to broilers intramuscularly 10–15 min after the breasts had been pre-treated with 25% sucrose solution. At 7 days after the second vaccination, chickens were challenged with 3×10⁴ sporulated oocysts of E. tenella BJ. The chickens were killed and the lesion scores of the ceca, the relative body-weight gains and the numbers of oocysts in the ceca of each group of chickens were calculated at day 8 post-inoculation. Results indicated that both pcDT and pcDET could induce protective immunity against coccidial challenge. Their use could obviously reduce oocyst output and alleviate chicken body-weight decrease due to coccidial infection. An anti-coccidial index of 160 was achieved with a treatment of 50 µg pcDET and 100 µg pcDT.     

Development and regulation of cell-mediated immunity in experimental leishmaniasis

The development of a Th1 response is critical for controlling many intracellular pathogens. Our laboratory has focused on the role IL-12 plays in initiating such a Th1 response following infection with the obligate intracellular protozoan, Leishmania. Infection of several mouse strains with L. major is associated with IL-12 production and the development of a Th1 response and resistance, although, interestingly, some species of Leishmania (L. mexicana and L. amazonenesis) fail to initiate a Th1 response in the same mouse strains. Consistent with these observations was our finding that IL-12 is an effective adjuvant for the induction of a Th1 response in leishmaniasis (1). Surprisingly, however, in spite of the fact that following resolution of a primary leishmanial infection there is substantial and long-lived resistance to reinfection, an effective prophylactic or therapeutic vaccine for human leishmaniasis does not exist. Our ability to induce a Th1 response in a primate Leishmania vaccine model, but not protection, suggests that long-term resistance to Leishmania requires more than simply initiating a Th1 response (2). Therefore, we recently expanded our studies to investigate how infection-induced resistance to Leishmania operates. We made the unexpected finding that IL-12 is required for L. major-infected mice to remain immune (3). We are now studying how IL-12 participates in maintaining cell-mediated immunity, and more broadly, how immunologic memory works in L. major-healed mice, as well as defining parasite factors that may block the development of cell-mediated immunity.     

Natural killer cells support the induction of protective immunity during dendritic cell-mediated vaccination against Leishmania major

Dendritic cell (DC)‐mediated vaccination against Leishmania major induces a parasite‐specific T helper 1 (Th1) response and long‐lasting protective immunity in susceptible mice. As the cytokine interleukin‐12 required for induction of this Th1 response is not derived from the transferred DC, but has to be produced by the vaccinated host, we examined cross‐presentation of transferred DC via resident DC of the host and cross‐activation with natural killer (NK) cells as mechanisms supporting the induction of protective immunity after DC‐mediated vaccination. Co‐culture with DC that had been conditioned ex vivo by loading with L. major lysate and stimulation with CpG‐containing oligodeoxynucleotides did not result in the activation of naive DC in vitro. Furthermore, L. major antigen from conditioned DC was not cross‐presented to a significant extent in vivo. In contrast, co‐culture of DC with NK cells led to cross‐activation of both cell populations with induction of interferon‐γ, which was dependent on the activation status of the conditioned DC. Transient depletion of NK cells during vaccination of L. major‐susceptible mice with conditioned DC resulted in reduced protection. Our findings indicate that cross‐presentation of conditioned DC after DC‐based vaccination against L. major plays a minor role in the induction of protective immunity. However, we demonstrated for the first time that the capacity of DC to mediate protection against L. major is supported by cross‐activation with NK cells of the host and NK‐cell‐derived interferon‐γ.