Antimicrobial Immunity Research Articles

CD1 Expression by Dendritic Cells in Human Leprosy Lesions: Correlation with Effective Host Immunity

A potential role for the CD1 family of lipid Ag-presenting molecules in antimicrobial immunity in vivo was investigated in human leprosy skin lesions. Strong induction of three CD1 proteins (CD1a, -b, and -c) was observed in dermal granulomas in biopsy samples of involved skin from patients with the tuberculoid form of leprosy or with reversal reactions, which represent clinical patterns of disease associated with active cellular immunity to Mycobacterium leprae. In contrast, lesions from patients with the lepromatous form of the disease who lack effective cell-mediated immunity to the pathogen did not show induction of CD1 proteins. Thus, expression of CD1 correlated directly with effective immunity to M. leprae, as assessed by the clinical course of infection. CD1a, -b, and -c could be induced to similar levels on monocytes from the blood of either tuberculoid or lepromatous leprosy patients. This suggested that the absence of expression in lepromatous lesions was most likely due to local factors at the site of infection as opposed to a primary defect of the CD1 system itself. The majority of cells expressing CD1 in leprosy lesions were identified as a population of CD83+ dendritic cells. Initial in vitro studies of the Ag-presenting function of CD1+CD83+ monocyte-derived dendritic cells showed that such cells were highly efficient APCs for CD1-restricted T cells. These results indicate that the CD1 system can be up-regulated in human infectious diseases in vivo, and may play a role in augmenting host defense against microbial pathogens.

Role of heat shock proteins in protection from and pathogenesis of infectious diseases.

Increased synthesis of heat shock proteins (hsp) occurs in prokaryotic and eukaryotic cells when they are exposed to stress. By increasing their hsp content, cells protect themselves from lethal assaults, primarily because hsp interfere with the uncontrolled protein unfolding that occurs under stress. However, hsp are not produced only by stressed cells; some hsp are synthesized constitutively and perform important housekeeping functions. Accordingly, hsp are involved in the assembly of molecules which play important roles in the immune system. It is not surprising that due to their wide distribution and their homology among different species, hsp represent target antigens of the immune response. Frequent confrontation of the immune system with conserved regions of hsp which are shared by various microbial pathogens can potentiate antimicrobial immunity. However, long-term confrontation of the immune system with hsp antigens which are similar in the host and invaders may convert the immune response against these host antigens and promote autoimmune disease. This review provides an overview of the role of hsp in immunity with a focus on infectious and autoimmune diseases.

Role of gamma delta T lymphocytes in immune response in humans and mice.

T lymphocytes recognize antigen through the T cell receptor. T cells expressing the gamma delta T cell receptor have been found in many species. Whereas murine alpha beta T cells are concentrated in the lymphoid organs, gamma delta T cells represent only a minor population in the adult thymus and peripheral lymphoid organs (less than 5% of the population). However, murine gamma delta cells predominate in epidermis, in epithelial layers of small intestine, in lung, and in female reproductive organs. In contrast, human gamma delta cells predominate in lymphoid organs. Despite extensive progress in the molecular characterization of the gamma delta T cell receptor and its genes, the physiological role of gamma delta T cells has remained elusive for many years. It is becoming now clear that, in contrast to alpha beta cells that recognize peptide/MHC complexes, gamma delta T cells appear to recognize unprocessed proteic antigens and, in humans, also a class of widely represented nonproteic antigens containing critical phosphate moieties. Similarly, it is now known that gamma delta cells can perform a vast array of immune effector functions and appear to play important roles in antimicrobial immunity as well as in chronic inflammatory reactions.

The T cell response against fungal infections

A variety of pathological conditions, including impaired immune function, is believed to underlie host susceptibility to fungal infections and to determine both the severity and the characteristics of the associated pathology. Although the redundancy and the interdependence of antifungal responses may not favor the proper dissection and appreciation of individual effector mechanisms, the T helper type 1/type 2 paradigm of acquired immunity to fungi is proving essential for a better understanding of the host response from a regulatory perspective. The recent understanding of the importance of the different T helper cell subsets in fungal infections and the increasing appreciation of the reciprocal regulation between the innate, humoral, and adaptive immune systems in the development of optimal antimicrobial immunity have offered us new clues which may lead to an understanding of T cell dependent immunity to fungi.

Gamma/delta and other unconventional T lymphocytes: what do they see and what do they do?

T lymphocytes recognize specific ligands by clonally distributed T-cell receptors (TCR). In humans and most animals, the vast majority of T cells express a TCR composed of an alpha chain and a beta chain, whereas a minor T-cell population is characterized by the TCR gamma/delta. Almost all of our knowledge about T cells stems from alpha/beta T cells and only now are we beginning to understand gamma/delta T cells. In contrast to conventional alpha/beta T cells, which are specific for antigenic peptides presented by gene products of the major histocompatibility complex, gamma/delta T cells directly recognize proteins and even nonproteinacious phospholigands. These findings reveal that gamma/delta T cells and alpha/beta T cells recognize antigen in a fundamentally different way and hence mitigate the dogma of exclusive peptide-major histocompatibility complex recognition by T cells. A role for gamma/delta T cells in antimicrobial immunity has been firmly established. Although some gamma/delta T cells perform effector functions, regulation of the professional and the nonprofessional immune system seems to be of at least equal importance. The prominent residence of gamma/delta T cells in epithelial tissues and the rapid mobilization of gamma/delta T cells in response to infection are consistent with such regulatory activities under physiological and pathologic conditions. Thus, although gamma/delta T cells are a minor fraction of all T cells, they are not just uninfluential kin of alpha/beta T cells but have their unique raison d'être.

Dissociation of demyelination and viral clearance in congenitally immunodeficient mice infected with murine coronavirus JHM

Infection of rodents with murine coronavirus JHM results in a subacute or chronic demyelinating disease which serves as a model for the human disease multiple sclerosis. Previous studies with JHMV have established a role for the immune system in both viral clearance and demyelination. To further clarify the role of the immune system in JHMV pathogenesis, several strains of congenitally immunodeficient mice were studied. Infection of immunocompetent C57BL/6 mice with JHMV resulted in severe paralysis and demyelination and complete clearance of infectious virus from the brain (C+D+ phenotype). In contrast, infected SCID mice showed little or no paralysis or demyelination and were unable to clear infectious virus (C-D- phenotype). Athymic nude mice and a proportion of mice lacking MHC Class I or II expression exhibited robust demyelination but did not completely clear infectious virus from the brain (C-D+ phenotype). These results are consistent with an immune-mediated mechanism for JHMV-induced demyelination, but indicate that the immune mechanisms which participate in demyelination and viral clearance are distinct. It may thus be possible to experimentally alter immunopathological responses without impairing antimicrobial immunity.

Costimulation and the regulation of antimicrobial immunity

The regulated expression of costimulatory molecules is a major factor limiting T-cell responses to self-antigens. However, the development of effective antimicrobial immunity requires that these molecules be induced on a variety of tissues, but most notably on macrophages. Here, Paul Kaye discusses the regulation of costimulatory molecules on macrophages and suggests that microbial interference in this process has important implications for immune regulation.

Deficient expression of co-stimulatory molecules on Leishmania-infected macrophages.

Co-stimulatory signals are necessary for the full activation of T cells for growth and effector function. As co-stimulatory molecules are normally regulated in their expression, it has been suggested that microorganisms enhance their expression on host antigen-presenting cells (APC), thus allowing efficient generation of anti-microbial immunity. We here describe experiments which demonstrate that infection of macrophages, both in vitro and in vivo, by the protozoan parasite Leishmania donovani fails to trigger expression of co-stimulatory molecules B7-1 and heat-stable antigen on these APC. Furthermore, infection with this parasite inhibits the macrophage response to normal regulatory signals, such as bacterial lipopolysaccharide. These changes in the cell surface are mirrored in functional studies of co-stimulation in vitro. Together, these data suggest a further facet of parasite interference in host immunity, but also indicate a potential new target for immunotherapy.

NADPH diaphorase staining suggests a transient and localized contribution of nitric oxide to host defence against an intracellular pathogen in situ.

Nitric oxide (NO) is formed constitutively in neurons by the constitutive enzyme NO synthase (cNOS) and acts as a neurotransmitter. It has already been shown that cNOS-containing neurons are identical to neurons staining for NADPH diaphorase and vice versa. Effector cells of the immune response produce high NO levels after appropriate stimulation and this NO is formed by inducible NO synthase (iNOS). The NO produced by macrophages is considered an important effector molecule of antimicrobial host defence. We have applied NADPH diaphorase staining for the detection of NO producing cells in situ during infection with an intracellular pathogen. Macrophages which produce NO in vitro are stained for NADPH diaphorase. Expression of iNOS mRNA and macrophage NADPH diaphorase staining was inhibited by iNOS-specific antisense oligonucleotides. These data suggest coincidental similarity between NADPH diaphorase activity and NO production by macrophages. Cells staining for NADPH diaphorase were identified in cryostat frozen sections of livers from mice infected with the intracellular pathogen, Listeria monocytogenes, and co-localized with cells labelled by MAC-1 mAbs. The purple-blue reaction product of NADPH diaphorase staining was visible in discrete granulomatous lesions but was absent from the liver parenchyma. Our results provide direct evidence for localized and transient participation of NO in antimicrobial immunity in the infected organ. This restriction may focus NO production to lesions, leaving unrelated tissue sites unaffected.

T cell-mediated cognate signaling of nitric oxide production by macrophages. Requirements for macrophage activation by plasma membranes isolated from T cells.

Macrophage generation of reactive nitrogen intermediates (RNI) represents a major effector mechanism in anti-microbial immunity and non-septic inflammatory reactions. The induction of macrophage RNI production has been demonstrated to require at least two signals which in microbial infections can be provided by interferon (IFN)-gamma and lipopolysaccharide (LPS). The current study demonstrates that, in the absence of LPS, T lymphocytes can provide cognate signal(s) which synergize with IFN-gamma in stimulating macrophage RNI production, as evidenced by the ability of plasma membranes from T cell clones to activate IFN-gamma-primed macrophages. Although viable resting T cells can activate IFN-gamma-primed macrophages by an interaction that is antigen specific, plasma membranes from resting T cells do not active macrophages. Plasma membranes from T cells activated by immobilized anti-CD3 were able to effectively induce RNI production in IFN-gamma-primed macrophages. However, in contrast to the antigen-specific interaction of macrophages with viable resting T cells, the activation of IFN-gamma-primed macrophages by membranes from activated T cells does not display antigen specificity. Plasma membranes from activated T helper TH2 and from activated TH1 cells were equally effective in activating IFN-gamma-primed macrophages, suggesting that the dominance of TH1 over TH2 cells in cell-mediated responses involving macrophage effectors is not a reflection of differences in their ability to interact with macrophages but rather is a reflection of their different pattern of cytokine production. These results suggest that the T cell-macrophage interaction involves reciprocal activation of both cells--an antigen-specific activation of the T cells which results in the acquisition of T cell membrane components involved in antigen-nonspecific stimulation of the macrophages.

Role of the mononuclear phagocyte as an antigen-presenting cell for human gamma delta T cells activated by live Mycobacterium tuberculosis.

gamma delta T cells, both human and murine, have been found to be highly responsive to mycobacterial antigens. However, the role and function of gamma delta T cells in the immune response to Mycobacterium tuberculosis remain largely unknown. In earlier studies, we demonstrated that monocytes infected with live M. tuberculosis were particularly effective inducers of human peripheral blood gamma delta T cells. The present studies were performed to further characterize the interaction between human mononuclear phagocytes, gamma delta T cells, and live M. tuberculosis, in comparison with CD4+ T cells. First, we found that resting gamma delta T cells expanded in vitro by live M. tuberculosis were specific for M. tuberculosis, and that heat killing and washing the mycobacteria removed the antigen(s) for gamma delta T cells. In contrast, the heat-killed mycobacteria retained significant antigenicity for CD4+ T cells. Second, live M. tuberculosis-expanded gamma delta T cells from healthy tuberculin-positive donors did not respond significantly to the antigens in M. tuberculosis culture filtrate, including the 65- and 71-kDa mycobacterial heat shock proteins. Third, the activation of gamma delta T cells by live mycobacteria was dependent on antigen-presenting cells, and mononuclear phagocytes were found to be very efficient antigen-presenting cells both for resting peripheral blood gamma delta T cells and for activated expanded gamma delta T cells. The mononuclear phagocyte carried the necessary costimulatory factors necessary for gamma delta T-cell proliferation. Fourth, the antigen repertoire and HLA requirements for CD4+ memory T cells and those for gamma delta T cells appear to be quite distinct from each other. CD4+ T cells recognized both soluble protein antigens and whole organisms in a class II major histocompatibility complex-restricted manner, whereas gamma delta T cells appeared to recognize only constituents associated with the whole organism and were not restricted by class I or class II major histocompatibility complex molecules. Finally, the assay system described to expand and purify responding CD4+ and gamma delta T cells after stimulation with live M. tuberculosis represented a simple approach to the direct comparison of these two T-cell populations in the interaction with mononuclear phagocytes infected with M. tuberculosis. Such studies provide insight not only into the relative roles of human CD4+ and gamma delta T cells in the human immune response to intracellular bacterial pathogens such as M. tuberculosis but also into the basic biologic role of human gamma delta T cells in antimicrobial immunity.

Modulation of natural killer and lymphokine-activated killer cell cytotoxicity by lactoferrin

Natural killer (NK) and lymphokine-activated killer (LAK) cell cytotoxic functions can be strongly augmented by the iron-carrier protein lactoferrin (LF). LF significantly enhances NK and LAK activities when added at the beginning of NK or LAK cytotoxicity assays. LF is effective in augmenting cytotoxic activities at concentrations as low as 0.75 microgram/ml, and higher concentrations of LF induce greater augmentation of NK and LAK. Iron does not appear to be essential for LF to increase NK and LAK, as depleting iron from LF with the chelator deferoxamine does not affect the capacity of LF to increase cytotoxicity. LF is known to have RNase enzymatic activity, and LF enhancement of NK and LAK can be blocked by RNA. However, LFs from two different sources with over 100-fold difference in RNase activity are equally effective in enhancing NK and LAK. Furthermore, purified non-LF RNase does not modulate NK or LAK activity and DNA is as effective as RNA in blocking LF augmentation of NK or LAK cytotoxicity. Therefore, the RNase activity is unlikely to be responsible for LF enhancement of the cytotoxicities. Newborn infants are known to have low NK activity and NK and LAK cells have been implicated in host defense against microbial infections. Thus, maternal milk-derived LF may have a role in boosting antimicrobial immunity in the early stages of life. In adults, LF released from neutrophils may enhance NK and LAK functions in the inflammatory process induced by microbial infections.

Aging and immunity to tuberculosis: Prolonged survival of old mice infected with Mycobacterium tuberculosis by adoptive immunization with memory-immune T lymphocytes

This study shows that memory immune T lymphocytes, harvested from young (3-month-old) mice infected intravenously with Mycobacterium tuberculosis and then exposed to protracted chemotherapy with isoniazid, are capable of adoptively protecting old (24 month) mice from a subsequent fatal challenge infection. Survival of such adoptively protected animals was prolonged, but did not extend beyond the mean survival time of uninfected old control mice. During this time the passively transferred memory T cell population retained their functional capacity to protect against subsequent tuberculosis infection. These data indicate, therefore, that reconstitution of decayed cell-mediated antimicrobial immunity in old mice in vivo with memory T cells is technically feasible, although the life span of the animal is not extended over that of control animals. They indicate, moreover, that the memory T cells remain functional in what some reports have considered a suppressive environment and show further that the macrophages with which the infused T cells interact in the aged host remain functionally able to express acquired resistance.

An age-related loss of the isogeneic barrier to the successful passive cell transfer of antimicrobial immunity in mice

The results of this study show that an isogeneic barrier to the successful adoptive immunotherapy of Mycobacterium tuberculosis infected mice is progressively lost as these animals age. This was shown in this study by the demonstration that increasing levels of transfered acquired specific resistance could be conferred on normal old recipients of greater than 22 months of age, whereas in young recipients such transfers were unsuccessful without the prior exposure of recipients to sublethal levels of whole-body gamma irradiation. These data indicate that strategies of adoptive immunotheraphy in the elderly may not have to overcome the age-related isogeneic physiological barrier to this procedure.

Fibronectin content in the milk and blood of mothers and in the blood of their newborns

The infant's resistance to infection is largely determined by the biologically active substances in the woman's milk: immunoglobulins, proteins of the complement system, interferon, lysozyme, lactoperoxidase, lactoferrin, etc. There are single works, which show the presence of fibronectin protein in women's milk. One of the main functions of this protein is its opsonic activity in phagocytosis reactions, which allows to consider it as a nonspecific protection factor capable of taking part in the formation of antimicrobial immunity of newborns.

Molecular mimicry of a carbohydrate epitope on a major surface glycoprotein of Trypanosoma cruzi by using anti-idiotypic antibodies.

The use of anti-idiotypic antibodies (Ab2) to induce anti-microbial immunity might be particularly advantageous with respect to responses directed against carbohydrate determinants, because it may not be feasible to reproduce these epitopes by recombinant DNA technology. In the present studies, rabbit Ab2 were produced against a recurrent BALB/c idiotype defined by a monoclonal antibody (WIC 29.26) with specificity for a carbohydrate epitope of a major surface glycoprotein of Trypanosoma cruzi. The Ab2 induced specific antibodies in mice, rabbits, and guinea pigs, and reacted with parasite-induced anti-T. cruzi antibodies from mice and rabbits as well as humans. The behavior of this Ab2 is therefore consistent with that of the antigen itself, and suggests that molecular mimicry of carbohydrate epitopes can be easily achieved.

Effect of aging on antimicrobial immunity: old mice display a normal capacity for generating protective T cells and immunologic memory in response to infection with Listeria monocytogenes.

Old (19 to 30 mo) and young adult (11 to 16 wk) AB6F1 mice of both sexes were compared in terms of their capacity to resist infection with Listeria monocytogenes. The LD50 was found to be two to four times higher for old than for young mice, and the time to death was longer for old mice. Enumeration of bacteria in the livers and spleens showed that old mice restricted growth of Listeria more effectively than young mice during the preimmune phase of infection, the difference being detectable as early as 12 to 24 hr after bacterial inoculation. Therefore, to ensure a similar level of infection in old and young mice, old mice had to be given a larger inoculum. Indeed, it was found that, provided the size of the bacterial inoculum was adjusted to make the level of immunizing infection the same, old mice generated similar levels of anti-Listeria immunity as young mice, as measured by their ability to generate splenic T cells capable of adoptively immunizing young recipients against lethal challenge infection. Furthermore, the level of memory immunity to reinfection 28 to 117 days after immunizing infection was similar in old and young mice. The results indicate, therefore, that old mice have no defect in their capacity to generate T cell-mediated anti-Listeria immunity.

5] Adoptive transfer

This chapter describes adoptive transfer as the transfer of immunity from one animal to another by live, immunocompetent cells as opposed to immune serum or preformed antibody. It explores that the principle of adoptive transfer showed delayed-type hypersensitivity to picryl chloride could be transferred from sensitized to normal guinea pigs with peritoneal exudate cells but not with serum. The chapter reviews that adoptive transfer was originally applied only to delayed-type hypersensitivity and transplantation immunity, but with the subsequent expansion of cellular immunology, it has been used to transfer virtually all types of immunity, including tumor immunity, auto-immunity, antimicrobial immunity, and anti-idiotypic immunity. It discusses that the first requirement for a successful adoptive transfer is that the primary host be adequately immunized and lymphoid cells be transferred at an appropriate time. Second, from the standpoint of histocompatibility, the secondary host must accept the transferred cells, at least temporarily. The chapter also explores that a specialized form of adoptive transfer which is frequently used to study tumor immunity is the Winn test.

Expression of cell-mediated antimicrobial immunity by mouse trophoblast monolayers.

Monolayers of mouse trophoblast cells were produced after short-term culture (two to four days) of ectoplacental cone cells derived from 7.5-day-old mouse conceptuses and were then tested for phagocytic activity. Following brief intervals of coincubation with the blood stage form of Plasmodium berghei, the parasite that causes rodent malaria, cultured trophoblast cells were found to phagocytose large amounts of parasitic material. In a manner similar to that of peritoneal macrophages, trophoblast cells ingested predominantly hemozoin pigment granules, while internalization of nonparasitized red blood cells occurred infrequently. Trophoblast-mediated phagocytosis was sensitive to the inhibitory effects of cytochalasin B. The expression of this form of immunelike function by midstage trophoblastic elements may play an important role during embryogenesis by protecting the fetoplacental unit from injury by invading microorganisms or by limiting congenitally acquired infections.

Aging and antimicrobial immunity. Lowered efficiency of protective T cells as a contributing factor for the decreased resistance of senescent mice to listeriosis.

Experimental murine listeriosis was used as a model to investigate the immunological basis for the age-associated decline in antimicrobial immunity. The reduced capacity of protective T cells from Listeria-immune senescent mice to adoptively immunize normal syngeneic recipients could not be attributed to inhibition of their activity by suppressor cells. Radiolabeled enriched splenic T cells from Listeria-immune young or senescent donors exhibited an identical distribution pattern after an intravenous infusion into young recipients. Moreover, cells from Listeria-immune young donors showed markedly greater protective capacity than cells from senescent immune donors whether the cells were transferred to young or senescent recipients. Dose-response analysis of protective T cells revealed that in response to immunizing infection (a) senescent mice generated 10-fold fewer protective T cells, and (b) protective T cells from senescent mice were 100-fold less efficient than cells from young mice.