Lysis of mycobacteria-infected monocytes by IL-2-activated killer cells: role of LFA-1

Comparative Diagnostic Utility of Neopterin and IFN-γ/IL-2 in Extrapulmonary Tuberculosis

Resurgence of TB has emphasized the need for newer methods of diagnosis. Extrapulmonary tuberculosis (EPTB), being paucibacillary, is a diagnostic dilemma. The aim of the present study was to correlate IFN-γ/IL-2 with neopterin in diagnosis of EPTB. Extrapulmonary specimens from 69 clinically diagnosed cases were stained by Ziehl-Neelsen and cultured on Lowenstein-Jensen medium for Mycobacterium tuberculosis. ELISA was used to assess serum IFN-γ, IL-2 and neopterin levels. Median serum levels of IFN-γ/IL-2 and neopterin were 3.22 and 21.6 nmol/L in clinically diagnosed EPTB cases and 0.52 and 4.20 nmol/L in healthy controls respectively (p < 0.001). Both IFN-γ/IL-2 and neopterin were significantly higher in culture positive (14.64 and 49.8 nmol/L) than culture negative cases (3.01 and 17.5 nmol/L) respectively (p < 0.05). IFN-γ/IL-2 was significantly higher in AFB smear positive cases (8.63) than smear negative cases (3.04) (p = 0.003), whereas no significant difference in neopterin levels was seen (p = 0.307). A positive correlation between IFN-γ/IL-2 and neopterin was seen in EPTB cases (spearman's rho = 0.453, p < 0.001), whereas in healthy controls no such correlation existed (spearman's rho = 0.018, p = 0.884). An urgent need for research in the field of biomarkers exists to utilize them as point of care test in the diagnosis of EPTB.

The Mycobacterium bovis BCG prime-Rv0577 DNA boost vaccination induces a durable Th1 immune response in mice

Tuberculosis remains a major global health problem and effective vaccines are urgently needed. In this study, we used the combined DNA- and protein-based vaccines of immunodominant antigen Rv0577 to boost BCG and evaluated their immunogenicity in BALB/c mice. Our data suggest that the booster vaccine may substantially enhance the immunogenicity of BCG and strengthen both CD4+ T cell-mediated Th1 and CD8+ T cell-mediated cytolytic responses. Compared with the protein-based vaccine, the DNA-based vaccine can induce more durable Th1 immune response, characterized by high levels of antibody response, proliferation response, percentages of CD4+/CD8+ and cytokine secretion in antigen-stimulated splenocyte cultures. In conclusion, we for the first time, developed a protein- and plasmid DNA-based booster vaccine based on Rv0577. Our findings suggest that antigen Rv0577-based DNA vaccine is immunogenic and can efficiently boost BCG, which could be helpful in the design of an efficient vaccination strategy against TB.

Immune markers and correlates of protection for vaccine induced immune responses

Vaccines have been a major innovation in the history of mankind and still have the potential to address the challenges posed by chronic intracellular infections including tuberculosis, HIV and malaria which are leading causes of high morbidity and mortality across the world. Markers of an appropriate humoral response currently remain the best validated correlates of protective immunity after vaccination. Despite advancements in the field of immunology over the past few decades currently there are, however, no sufficiently validated immune correlates of vaccine induced protection against chronic infections in neither human nor veterinary medicine. Technological and conceptual advancements within cell-mediated immunology have led to a number of new immunological read-outs with the potential to emerge as correlates of vaccine induced protection. For T(H)1 type responses, antigen-specific production of interferon-gamma (IFN-γ) has been promoted as a quantitative marker of protective cell-mediated immune responses over the past couple of decades. More recently, however, evidence from several infections has pointed towards the quality of the immune response, measured through increased levels of antigen-specific polyfunctional T cells capable of producing a triad of relevant cytokines, as a better correlate of sustained protective immunity against this type of infections. Also the possibilities to measure antigen-specific cytotoxic T cells (CTL) during infection or in response to vaccination, through recombinant major histocompatibility complex (MHC) class I tetramers loaded with relevant peptides, has opened a new vista to include CTL responses in the evaluation of protective immune responses. Here, we review different immune markers and new candidates for correlates of a protective vaccine induced immune response against chronic infections and how successful they have been in defining the protective immunity in human and veterinary medicine.

Cytokine and chemokine responses to selected early secreted antigenic target-6 and culture filtrate protein-10 peptides in tuberculosis

Cytokine [tumor necrosis factor-α, interleukin-2 (IL-2), IL-4] and chemokine [regulated upon activation normal T cell expressed and secreted (RANTES), monocyte chemoattractant protein-1] responses to selected early secreted antigenic target-6 (ESAT-6) and culture filtrate protein-10 (CFP-10) peptides were studied in healthy household contacts and patients with pulmonary tuberculosis (PTB). It was observed that Th1 cytokines and chemokine RANTES positive T cells were elevated in response to the peptides Esp1, Esp6, Cfp6, and Cfp8 in healthy household contacts. IL-4 positive T cells were enhanced by Esp1 and Esp6 in PTB. Monocyte chemoattractant protein-1 positive monocytes increased in response to the peptides Esp1, Esp6, Cfp8, and Cfp9 in PTB. These peptides deserve attention for further immune studies.

Immunological options for the treatment of tuberculosis: evaluation of novel therapeutic approaches

The emergence of multidrug-resistant tuberculosis strains and the coinfection with HIV, together with advances in immunology, have led to renewed interest regarding ways to exploit the immune responses against Mycobacterium tuberculosis therapeutically. Here we review the fundamentals of tuberculosis therapy in view of the epidemiological and clinical challenges, and explore the experience with immune-based therapies for the treatment of active tuberculosis. These immune-based therapies are discussed here with the aim of assessing their potential use as adjuncts to chemotherapy.

Putting the natural killer cell in its place

Natural killer (NK) cells were originally described as 'null' lymphocytes, but we have increasing evidence of their role in recognizing pathogen, and our knowledge of NK cell receptors continues to expand exponentially. Human NK cells have many receptors for human leucocyte antigen (HLA) class I. These killer immunoglobulin-like receptors (KIRs) and CD94/NKG2 receptors can signal in both positive and negative ways to regulate NK cell functions. The inhibitory receptors are the best characterized, but even in these cases much of their functional biology remains elusive. In this review, some recent advances in terms of the three-immunoglobulin (3Ig)-domain KIRs are discussed. Natural cytotoxicity receptors (NCRs) are among the activatory receptors found on NK cells. While pathogen ligands for these receptors have been described, endogenous ligands remain elusive. NCRs and NKG2D, a receptor for stress-induced antigens, appear to play complementary functional roles in terms of NK cell activation. More recently described on NK cells are the Toll-like receptors. In particular, these receptors of the innate immune system allow NK cells to directly sense pathogen, and their ligation on accessory cells indirectly activates NK cells through cytokine production. It is becoming clear that none of these receptor systems functions in isolation and that it is the sum of the signals (which will reflect the pathogenic situation), in addition to the cytokine milieu, that will direct NK cell activation. The resulting cytotoxicity, cytokine production and direct cell-cell regulatory interactions with other cells of the immune system, for example dendritic cells, ultimately determine the role of the NK cell in the context of an overall immune response.

Combinations of anti-LFA-1, everolimus, anti-CD40 ligand, and allogeneic bone marrow induce central transplantation tolerance through hemopoietic chimerism, including protection from chronic heart allograft rejection

Central transplantation tolerance through hemopoietic chimerism initially requires inhibition of allogeneic stem cell or bone marrow (BM) rejection, as previously achieved in murine models by combinations of T cell costimulation blockade. We have evaluated LFA-1 blockade as part of regimens to support mixed hemopoietic chimerism development upon fully allogeneic BALB/c BM transfer to nonirradiated busulfan-treated B6 recipient mice. Combining anti-LFA-1 with anti-CD40 ligand (CD40L) induced high incidences and levels of stable multilineage hemopoietic chimerism comparable to chimerism achieved with anti-CD40L and everolimus (40-O-(2-hydroxyethyl)-rapamycin) under conditions where neither Ab alone was effective. The combination of anti-LFA-1 with everolimus also resulted in high levels of chimerism, albeit with a lower incidence of stability. Inhibition of acute allograft rejection critically depended on chimerism stability, even if maintained at very low levels around 1%, as was the case for some recipients without busulfan conditioning. Chimerism stability correlated with a significant donor BM-dependent loss of host-derived Vbeta11(+) T cells 3 mo after BM transplantation (Tx). Combinations of anti-CD40L with anti-LFA-1 or everolimus also prevented acute rejection of skin allografts transplanted before established chimerism, albeit not independently of allospecific BMTx. All skin and heart allografts transplanted to stable chimeras 3 and 5 mo after BMTx, respectively, were protected from acute rejection. Moreover, this included prevention of heart allograft vascular intimal thickening ("chronic rejection").

An in vitro model for the lepromatous leprosy granuloma: fate of Mycobacterium leprae from target macrophages after interaction with normal and activated effector macrophages

The lepromatous leprosy granuloma is a dynamic entity requiring a steady influx of macrophages (Mphi) for its maintenance. We have developed an in vitro model to study the fate of Mycobacterium leprae in a LL lesion, with and without immunotherapeutic intervention. Target cells, consisting of granuloma Mphi harvested from the footpads of M. leprae-infected athymic nu/nu mice, were cocultured with normal or IFN-gamma-activated (ACT) effector Mphi. The bacilli were recovered and assessed for viability by radiorespirometry. M. leprae recovered from target Mphi possessed high metabolic activity, indicating a viable state in this uncultivable organism. M. leprae recovered from target Mphi incubated with normal effector Mphi exhibited significantly higher metabolism. In contrast, bacilli recovered from target Mphi cocultured with ACT effector Mphi displayed a markedly decreased metabolic activity. Inhibition by ACT Mphi required an E:T ratio of at least 5:1, a coculture incubation period of 3-5 days, and the production of reactive nitrogen intermediates, but not reactive oxygen intermediates. Neither IFN-gamma nor TNF-alpha were required during the cocultivation period. However, cell-to-cell contact between the target and effector Mphi was necessary for augmentation of M. leprae metabolism by normal effector Mphi as well as for inhibition of M. leprae by ACT effector Mphi. Conventional fluorescence microscopy and confocal fluorescence microscopy revealed that the bacilli from the target Mphi were acquired by the effector Mphi. Thus, the state of Mphi infiltrating the granuloma may markedly affect the viability of M. leprae residing in Mphi in the lepromatous lesion.

Lysis of salmonella typhi intracellularly infected U937 cells by human natural killer cells: effect of protein kinase inhibitors

We examined the effect of Salmonella typhi (wild-type Ty2 and mutant strain TYT1231)-infected U937 cells on natural killer cell (NKC) cytotoxicity of peripheral blood mononuclear cells (PBMCs) and highly purified NKC (HPNKCs; CD16(+)/CD56(+) > 95%; the rest corresponding to CD3(+) T cells). We also analyzed the possible role of various protein kinases involved in natural cytotoxicity on these processes. PBMC cytotoxicity against S typhi-infected U937 cells was significantly higher (paired Student t test; P < 0.05) than its lytic effect against noninfected cells (control) at the various effector-to-target cell ratios used (30:1 [24.4 +/- 9.7, 25.1 +/- 11.8, and 17.5 +/- 8.6]; 50:1 [26.6 +/- 9.7, 26.7 +/- 12.8, and 21.2 +/- 7.5] and 70:1 [32.4 +/- 14.4, 30.1 +/- 12.4, and 23.1 +/- 7.2], respectively). PBMC NKC activity seemed to be dependent on such ratios and was similar against both Salmonella strains studied. Approximately half of the individual samples tested (n = 12; 8 male and 4 female subjects of comparable age) showed at least a 20% specific lysis increase against their own control; essentially no changes or smaller increases in NKC activity were observed in all other samples. Similar results were obtained using HPNKCs as effector cells (5:1 ratio [38.9 +/- 12.3, 43.3 +/- 11.2, and 27.5 +/- 4.9] and 10:1 ratio [51.3 +/- 9.1, 46.1 +/- 9.8, and 37.7 +/- 15.5, respectively]). In general, specimens significantly lysed after incubation with PBMCs responded in a similar manner to a challenge with HPNKCs. PBMC and HPNKC cytotoxicity against S typhi wild-type-infected U937 cells was significantly decreased in a dose-dependent manner by the addition of genistein (50-200 micromol) or GFX (0.5-2.0 micromol) to the cytotoxicity assay mixture. NKC activity was almost completely inhibited at the highest genistein and GFX concentrations. In similar experiments, wortmannin (100-500 nmol) failed to inhibit PBMC cytotoxicity and significantly decreased HPNKC activity only at the highest concentration tested. These results show that in the process of NKC recognition and lysis of S typhi-infected U937 cells, there is not a requisite for full bacterial intracellular survival capacity and that S typhi-infected U937 cells are a significantly better target than noninfected U937 cells. NKC signaling pathways activated during the S typhi-infected U937 cell recognition and lysis process are mainly protein tyrosine kinase and protein kinase-C, and they can be blocked by the same protein kinase inhibitors known to inhibit natural cytotoxicity.

Treatment of infections in the patient with Mendelian susceptibility to mycobacterial infection

Cytokines are increasingly used for the therapy of infections in patient populations with special defects in immunity (chemotherapy, bone marrow transplantation, chronic granulomatous disease). The recognition of multiple defects in the systems of the interferon-gamma (IFN-gamma) receptor, interleukin-12 (IL-12) receptor and IL-12 p40 emphasizes the critical roles that cytokines play in preventing and clearing infection. The cases of patients with partially responsive IFN-gamma receptors (autosomal dominant and partial defects) are ideal candidates for successful cytokine prophylaxis and therapy. Better understanding of the critical elements of the cytokine pathways may show us ways to circumvent these defects with complementary cytokine cascades.

Effect of Salmonella typhi wild type and O-antigen mutants on human natural killer cell activity

We investigated the effect of glutaraldehyde-fixed Salmonella typhi Ty2 (Vi(-)) wild-type (World Health Organization's vaccine strain) and mutant strains MEI028 (rough, O-antigen(-)) and MEI012 [smooth (O-antigen(+)95%), immunomagnetically isolated NK cell preparations. Incubation of PBMC with each and every one of the S. typhi strains studied consistently and significantly, increased this cellular immune function, as well as the supernatant level of the various cytokines tested e.g. IFN-gamma, TNF-alpha, IL-10 and IL-12 (ELISA). In similar experiments, a significant increase in the cytolytic activity of HPNK cells was elicited by S. typhi Ty2 but not by mutant strain MEI028; neither of the cytokines assayed (IFN-gamma and TNF-alpha) was detected in the supernatant. Our results suggest that S. typhi O-antigen plays an essential role in a mechanism resulting in the direct activation of NK cell activity in HPNK cell preparations. However, the relative quantitative significance of this antigen in the direct stimulation of NK cell cytotoxicity expression in PBMC samples is less clear, as it appears that in this case bacterial-induced monocyte-released cytokines plays a most important role. Incubation with S. typhi Ty2 or MEI028 elicited significant expression of CD69, an early marker of NK cell activation, in PBMC but not in HPNK cell samples (flow cytometry); in similar experiments, the expression of CD16/56 and activation marker CD25 remained essentially unchanged.

Cell-mediated immune responses and cytotoxicity to mycobacterial antigens in patients with tuberculous pleurisy in Brazil

Evaluating human immune response to defined Mycobacterium tuberculosis antigens in patients with different clinical forms of tuberculosis may help in elucidating pathogenesis and in vaccine development. In the present report we evaluated the lymphocyte proliferation, cytokine production and natural killer cell cytotoxicity as parameters to screen four mycobacterial recombinant antigens. Pleural fluid mononuclear cells (PFMC) and peripheral blood mononuclear cells (PBMC) from 13 HIV-negative patients with tuberculous pleurisy, living in a tropical region of Brazil were used in these assays. Crude M. tuberculosis antigen and recombinant 70-, 65- and 38-kDa mycobacterial antigens, induced greater proliferation in PFMC than in PBMC. IFN-gamma, TNF-alpha, IL-4 and IL-10 were evaluated in the PFMC supernatants stimulated by these antigens. Both crude and 70-kDa antigens induced higher levels of IFN-gamma, TNF-alpha and IL-10. There was a significant positive correlation between IFN-gamma and the proliferative response induced by crude M. tuberculosis antigen, and an inverse correlation was identified between IL-10 and cell proliferation. IL-4 was not detected in the supernatants of pleural fluid mononuclear cell cultures stimulated by either crude, or recombinant antigens. TNF-alpha was detected in variable amounts in supernatants of PFMC stimulated by all antigens tested. Natural killer cytotoxicity was induced by both crude and 70-kDa antigen. Our results demonstrate that cells present at the site of disease recognized three of the antigens screened, as shown by lymphocyte proliferation and production of regulatory and inflammatory cytokines, and the results obtained with PFMC were consistently higher than those obtained with homologous PBMC.

Immunobiology of Mycobacterium avium infection

Infection caused by organisms of the Mycobacterium avium complex is diagnosed in 50% to 60% of AIDS patients with the advanced stage of disease. Mycobacterium avium is an environmental bacterium that gains access to the host through both the gastrointestinal tract and the respiratory tract. After crossing the mucosal barrier Mycobacterium avium disseminates, infecting chiefly mononuclear phagocytes of the reticuloendothelial system. A number of cells of the immune system such as CD4+ T cells, natural killer cells and macrophages have been shown to be involved in the host response to Mycobacterium avium. The interaction between Mycobacterium avium and macrophages results in the production of immune-suppressive cytokines that inhibit the effector function of TH1 subtype CD4+ T cells, natural killer cells and macrophages, possibly allowing survival of Mycobacterium avium. Some cytokines such as tumor necrosis factor alpha and granulocyte-macrophage colony-stimulating factor have been shown to induce mycobacteriostatic activity and mycobactericidal activity in infected macrophages. Over the next few years, much new information will certainly be gleaned about host-pathogen interactions, which will lead to a better understanding of the disease and possibly to the design of new forms of therapy.

Dysfunctional monocytes from a patient with disseminated Mycobacterium kansasii infection are activated in vitro and in vivo by GM-CSF

A 27 year-old woman presented with disseminated infection due to Mycobacterium kansasii. Signs and symptoms of disseminated infection persisted despite the administration of multiple antimycobacterial agents to which her organism was sensitive for 15 months. She was seronegative for HIV-1 and functional studies of T and B lymphocytes and granulocytes failed to demonstrate any abnormality. Peripheral blood monocytes proved abnormally permissive to the intracellular growth of Mycobacterium avium and M. kansasii, and expressed normal number of receptors to interferon-gamma, but reduced numbers of receptors to granulocyte monocyte colony stimulating factor and tumor necrosis factor. These defects were partially reversed with in vitro exposure of her cells to recombinant GM-CSF. In addition, administration of recombinant human GM-CSF in vivo (250 mg/M2 per day) for 10 days armed her circulating monocytes as evidenced by increased production of O2- in response to phorbol esther and, when infected ex vivo with M. kansasii, enhanced inhibition of intracellular growth compared with pre-therapy monocytes. These defects reappeared with discontinuation of GM-CSF and resolved with its re-administration. While a salutary clinical and microbiologic effect was difficult to assess, administration of GM-CSF in vivo was associated with in vitro activation of monocytes and enhanced mycobactericidal activity in this patient with a defect in monocyte function.

The Mycobacterium avium complex

Mycobacterium avium complex (MAC) disease emerged early in the epidemic of AIDS as one of the common opportunistic infections afflicting human immunodeficiency virus-infected patients. However, only over the past few years has a consensus developed about its significance to the morbidity and mortality of AIDS. M. avium was well known to mycobacteriologists decades before AIDS, and the MAC was known to cause disease, albeit uncommon, in humans and animals. The early interest in the MAC provided a basis for an explosion of studies over the past 10 years largely in response to the role of the MAC in AIDS opportunistic infection. Molecular techniques have been applied to the epidemiology of MAC disease as well as to a better understanding of the genetics of antimicrobial resistance. The interaction of the MAC with the immune system is complex, and putative MAC virulence factors appear to have a direct effect on the components of cellular immunity, including the regulation of cytokine expression and function. There now is compelling evidence that disseminated MAC disease in humans contributes to both a decrease in the quality of life and survival. Disseminated disease most commonly develops late in the course of AIDS as the CD4 cells are depleted below a critical threshold, but new therapies for prophylaxis and treatment offer considerable promise. These new therapeutic modalities are likely to be useful in the treatment of other forms of MAC disease in patients without AIDS. The laboratory diagnosis of MAC disease has focused on the detection of mycobacteria in the blood and tissues, and although the existing methods are largely adequate, there is need for improvement. Indeed, the successful treatment of MAC disease clearly will require an early and rapid detection of the MAC in clinical specimens long before the establishment of the characteristic overwhelming infection of bone marrow, liver, spleen, and other tissue. Also, a standard method of susceptibility testing is of increasing interest and importance as new effective antimicrobial agents are identified and evaluated. Antimicrobial resistance has already emerged as an important problem, and methods for circumventing resistance that use combination therapies are now being studied.

Antigen-presenting cell types

Different antigen-presenting cells elicit responses in different T-cell populations for primary activation, secondary stimulation and cytotoxic effector functions. Maturing bone marrow derived dendritic cells may acquire and process antigens, transport them to lymph nodes and activate naive T cells located there. By contrast, follicular dendritic cells, acquiring antigen-antibody complexes, maintain 'memory' via B-cell activation. Effector memory T cells recognize various tissue cells bearing antigen and we speculate that they may also target specialized antigen-presenting dendritic populations.

Human lymphokine-activated killer cells are cytotoxic against cells infected with Toxoplasma gondii

Experiments were conducted to determine whether human lymphokine-activated killer (LAK) cells are cytotoxic against cells infected with Toxoplasma gondii. Nylon wool nonadherent (NWNA) peripheral blood lymphocytes, as well as purified natural killer cell (NK) (CD3- CD16+ CD56+) and T (CD3+ CD16- CD56-) cells obtained from five healthy T. gondii seronegative volunteers exhibited minimal cytotoxic activity against T. gondii-infected cells. When standard LAK (S-LAK) cell preparations were induced by incubation of NWNA cells with recombinant interleukin 2, induction of remarkable cytotoxic activity against T. gondii-infected cells. When standard in LAK cell preparations from each of the volunteers. The phenotype of the LAK precursor and effector cells varied depending on the target cell used. Whereas the precursor and the effector cells of most of the LAK activity against K562 and Daudi cells were cells with NK phenotype, when T. gondii-infected cells were used as targets, both cells with NK and T cell phenotypes were precursors and effectors of the lysis. When cytotoxic activity of S-LAK cells was compared with the activity of adherent LAK (A-LAK) cells, A-LAK cells displayed higher cytotoxic activity against T. gondii-infected cells, as well as against K562 and Daudi cells. Cold target inhibition experiments suggested that there is a subset of LAK effector cells capable of lysing both T. gondii-infected cells and Daudi cells, whereas other subsets preferentially or exclusively lyse one of these target cells.

Lymphokine-activated killer cell regulation of T-cell-mediated immunity to Candida albicans

Monocytes are important accessory cells in the activation of T cells for specific antigen recognition yet little is known of their regulation. We demonstrated here that interleukin-2 (IL-2)-induced human lymphokine-activated killer (LAK) cells can inhibit monocyte antigen presentation, depending on the state of differentiation of the monocytes. Adherent monocytes cultured for 4 days in medium or granulocyte-macrophage colony-stimulating factor (GM-CSF) were found to equally process and present intact Candida albicans to autologous Percoll gradient-isolated T cells, as measured by [3H]thymidine uptake. However, only the GM-CSF-cultured monocytes were functionally inhibited by autologous 4-day IL-2-induced LAK cells. Even soluble candidal cell wall mannoprotein antigens could not be presented by these monocytes after exposure to LAK cells. Pretreatment of these monocytes with LAK cells for 1 h, followed by subsequent removal of the nonadherent LAK cells, was sufficient to cause significant inhibition, with maximal inhibition observed after 4 h. Northern (RNA) blot analysis indicated that mRNA expression for IL-1 alpha and IL-1 beta in response to C. albicans stimulation was also down-regulated in GM-CSF-cultured monocytes exposed to LAK cells. Interestingly, freshly isolated, Percoll gradient-purified large granular lymphocytes did not suppress antigen presentation in GM-CSF-treated monocytes. Another important finding was the inability of LAK cells to suppress the ability of freshly isolated or gamma interferon-cultured monocytes, which are resistant to LAK cell-mediated lysis, to present antigen to T cells. In contrast, IL-3 was similar to GM-CSF in inducing LAK cell susceptibility in monocytes. Taken together, these results indicated that IL-2 can induce LAK cells to down-regulate antigen presentation function in a select set of monocytes that have been activated by colony-stimulating factor (GM-CSF and IL-3) but not by gamma interferon. LAK cells may therefore play an important role in regulation of monocytes and their function, depending on their differentiation state.

Mycobacterial induction of activated killer cells: possible role of tyrosine kinase activity in interleukin-2 receptor alpha expression

Mycobacterium avium is an intracellular opportunistic pathogen commonly seen in AIDS patients. M. avium-infected monocytes have been recently shown to be lysed by interleukin-2 (IL-2)-activated killer cells. Since some bacterial products can directly augment natural killer activity, we examined the ability of these microorganisms to induce killer cell activity. Coculture of M. avium with large granular lymphocytes (LGL) was found to augment the ability of LGL to lyse both tumor cells and bacterially infected autologous monocytes. The induction of tumoricidal activity by M. avium was only partially neutralized by the presence of anti-IL-2 antibodies, indicating that both IL-2-dependent and IL-2-independent mechanisms are responsible for activation of killer cells. Furthermore, only the direct interaction between bacterium and LGL could induce the expression of both IL-2 receptor alpha protein and mRNA, an effect which was abrogated by the presence of genistein, a tyrosine kinase inhibitor. Thus, M. avium was seen to induce killer cells, an activity that is concomitant with the up-regulation of IL-2 receptor alpha, or Tac antigen, expression and which involves signal transduction mechanisms mediated by tyrosine kinase activity.

Recognition of heterogeneous lymphokine-activated killer (LAK) receptors on Kaposi's sarcoma cells, endothelial cells, and monocytes/macrophages: Evidence of distinct LAK-cell antigen on Kaposi's sarcoma cells?Potential for use of LAK cells for immunotherapy

The purpose of this study was to determine the potential use of lymphokine-activated killer (LAK) cells against Kaposi's sarcoma (KS) cells. We used chromium release cold-target inhibition assay for understanding the expression of heterogeneous LAK-cell antigens (Ags) on KS cells, endothelial cells (ECs), and monocytes/macrophages (M phi) which could allow for the utilization of LAK-cell immunotherapy in KS without side effects. Our data show that (i) all three cell types express the CD18 Ag of LFA-1 or Leu-CAM, (ii) rare KS cells from eyes cannot cold target-inhibit ECs, (iii) KS cells express a distinct LAK-cell Ag, which we have called LAK-KS Ag, and (iv) LAK-KS Ag allows for cold-target inhibition between different KS cells. The identification of LAK-KS Ag and a monoclonal antibody capable of inhibiting lysis of ECs and M phi without obstructing LAK-KS Ag would be important.

Dissociation of macrophage cytolysis and ability to transfer anti-listeria resistance by concanavalin A-stimulated spleen cells

In this study, we determined whether spleen cells from Listeria monocytogenes-immunized mice were cytolytic for Listeria-infected macrophages. Spleen cells freshly obtained from immunized donors were unable to lyse Listeria-infected macrophages unless they were first stimulated in vitro for 2-3 days with Concanavalin A (ConA) or L. monocytogenes. Spleen cells from non-immunized mice developed cytolytic activity after incubation with ConA, but not with L. monocytogenes. Cytolytic spleen cells demonstrated an equivalent ability to lyse uninfected and Listeria-infected thioglycollate elicited peritoneal macrophages. Maximal cytolysis required co-incubation of effector and target cells for 18-20 h. Spleen cell culture supernatants did not lyse macrophages, suggesting that cytolysis required direct contact. Preincubation of immune spleen cells with ConA decreased their ability to transfer anti-listeria resistance in the spleens, but not the livers of recipient mice. Depletion of CD4+ or CD8+ cells did not significantly reduce the ability of ConA-incubated Listeria-immune spleen cells to transfer resistance. Despite being cytolytic for Listeria-immune infected macrophages, ConA-stimulated non-immune spleen cells did not transfer anti-listeria resistance. These results indicate that cytolytic cells can be generated by short-term incubation of spleen cells with antigen or mitogen. The dissociation between in vitro cytolytic activity and ability to transfer protection, however, suggests that the two biological activities are not inextricably linked.

Cytokine activation of killer cells in mycobacterial immunity

Mycobacterium avium-intracellulare (MAI) is an ubiquitous soil contaminant that rarely causes disseminated disease in adults, regardless of immunological status. In AIDS patients, however, this microorganism invades virtually every tissue and organ, and most conventional chemotherapeutic agents are usually ineffective against MAI. We report here that monocytes, in which MAI has established an intracellular parasitic stage, appear to be under the control of natural killer (NK) cells. Autologous large granular lymphocytes (LGL), purified from human peripheral blood mononuclear cells (PBMC), were capable of efficiently lysing MAI-infected monocytes in a 5 hr 51Cr-release assay. More importantly, interleukin 2 (IL-2) was able to activate the LGL to a high degree of lysis of infected monocytes. Additionally, 3 to 4 days of incubation of LGL with MAI resulted in the induction of killer cells capable of killing bacterially-infected monocytes, as well as tumor cells. Northern blot analysis of RNA from MAI-stimulated LGL revealed specific messages for both IL-2 receptor proteins (p55 and p70). Thus, MAI can directly activate killer cells, which may therefore play a role in containment of MAI infection by lysis of parasitized monocytes before the bacteria can multiply and spread to other sites.

Rosacea-like lesions due to familial Mycobacterium avium-intracellulare infection

Mycobacterium avium-intracellulare (MAI) is a non-tuberculous, nonlepromatous or "atypical" mycobacterium now seen frequently in patients with acquired immunodeficiency syndrome (AIDS). In the past decade, the incidence appears to have increased in non-AIDS patients. Although cutaneous involvement is rare, two brothers without detectable immune defects who both presented with cutaneous MAI infection are described; the older brother also has disseminated disease. The cutaneous presentation of MAI, as well as immune and genetic defects that may predispose to mycobacterial infection, are discussed.

Mycobacterium leprae renders Schwann cells and mononuclear phagocytes susceptible or resistant to killer cells

Acquired resistance to Mycobacterium leprae, the etiologic agent of leprosy, crucially depends on cellular immune mechanisms. In addition to interleukin-mediated helper functions, killer mechanisms seem to be involved. This study addresses the question of how M. leprae render mononuclear phagocytes and Schwann cells, its natural targets, susceptible or resistant to killer cells. Killer activities were stimulated in peripheral blood mononuclear cells from healthy individuals by incubation with mycobacteria plus interleukin-2. These cells lysed Schwann cells and mononuclear phagocytes which had been pulsed with dead M. leprae, while unpulsed targets remained virtually unaffected. Importantly, targets infected with viable M. leprae were not lysed; furthermore, infection with viable M. leprae as well as gamma interferon stimulation or heat shock caused resistance in otherwise susceptible targets which had been pulsed with dead M. leprae. Thus, M. leprae markedly influenced the effect of killer cells on Schwann cells and mononuclear phagocytes.

Gamma interferon in experimental leprosy

We have shown that preactivated MACs are able to cope with newly acquired leprosy bacilli, and a high intracellular burden of live M. leprae induces a refractory response of the host MAC to activation by IFN-gamma. Our studies underscore the fact that MAC function in LL is dependent on localized conditions, influenced by the high intracellular burden of leprosy bacilli and, in part, involving the production of prostanoids. These findings preclude inferences about the function of granuloma MAC s in leprosy based on the responses of MACs from other easily accessible anatomical compartments such as the peritoneal cavity or peripheral blood. We feel that the clearance of bacilli from the LL lesion as a consequence of local immunotherapeutic measures or chemotherapy likely depends on the influx of new competent MAC rather than the activation of resident lepromatous MACs.

Lysis of human alveolar macrophages by lymphokine-activated killer cells

In order to determine if human LAK cells were cytotoxic against autologous AM phi, we studied the ability of human peripheral blood MNCs, stimulated in vitro with recombinant human IL-2, to lyse AM phi in a four-hour 51Cr-release assay. These cells showed significant cytotoxicity against autologous AM phi. The AM phi which had been cultured for four days served as better targets than freshly isolated AM phi. Kinetic study showed that the lysis of AM phi was proportional to the incubation time of MNCs with IL-2 and that LAK cells against AM phi required two days of in vitro culture with IL-2 for their induction. Freshly isolated MNCs did not lyse AM phi but did lyse K562 target cells, indicating that AM phi are natural killer-resistant. The phenotypes of effector cells against AM phi were found to be CD8+ or CD16+ (or both). These studies indicate that IL-2 can generate LAK cells against autologous AM phi, and this cytolytic activity must be taken into account when IL-2 or LAK cells are used for immunomodulation in patients with cancer.

Mycobacterium avium-Mycobacterium intracellular complex-induced suppression of T-cell proliferation in vitro by regulation of monocyte accessory cell activity

Heat-killed whole Mycobacterium avium-Mycobacterium intracellulare complex (MAC) and its lipid component impaired the capacity of human peripheral blood mononuclear cells to proliferate in vitro in response to concanavalin A (ConA), purified protein derivative of tuberculin (PPD), and to a lesser degree, phytohemagglutinin stimulation. Inhibition by MAC was not contingent upon prior exposure of the donor to MAC or other mycobacteria and occurred with lymphocytes from tuberculin-negative as well as -positive subjects. The suppression was not due to the toxicity of MAC. The suppression by MAC was not blocked by indomethacin. Adherent cell depletion and cell mixing experiments with T cells indicated that monocytes and not T cells were a major contributor to the immunosuppression observed. However, neither interleukin-1 production nor the expression of HLA-DR (Ia antigen) by monocytes was suppressed by MAC treatment. On the other hand, treatment of monocytes with MAC or MAC-derived lipid resulted in significant decreases in CD11b, a member of the leukocyte function-associated molecule-1 and LeuM3 (CD14) molecule. Anti-CD18 (beta-chain of the leukocyte function-associated molecule-1 family) monoclonal antibody had suppressive effects on ConA- and PPD- but not phytohemagglutinin-induced in vitro lymphocyte blastogenesis. We suggest that MAC and MAC-derived lipid suppress the ConA- and PPD-induced T-cell proliferations by blocking the expression of accessory molecules on the surfaces of monocytes which might be involved in nonspecific monocyte-T-cell interactions and not by inhibiting either monocyte Ia antigen expression or interleukin-1 production by monocytes.

Cytokine modulation of Mycobacterium tuberculosis growth in human macrophages

This study was concerned with the handling of ingested tubercle bacilli by normal human macrophages. Intracellular growth was determined after exposure of macrophages to viable bacilli in vitro and the effect of various cytokines, alone or in combination, on bacilli growth/survival was determined. It was found that Mycobacterium tuberculosis (M.tb) grew quite readily in untreated cultured human macrophages. Treatment with soluble factors showed that a crude lymphokine containing supernatant elicited with Concanavalin A (Con A) was ineffective at reducing growth of M.tb in vitro; similarly a crude lymphokine preparation from M.tb lysate-stimulated mononuclear cells failed to induce any mycobacteriostatic activity in human monocyte-derived macrophages. Recombinant cytokines were then evaluated for their ability to modulate growth of the tubercle bacilli in human macrophages. Recombinant interferon-gamma (IFN-gamma), interleukin-2 (IL-2) and recombinant interleukin 4 (IL-4) were all ineffective at modifying M. tuberculosis growth in human macrophages. Recombinant tumour necrosis-alpha (TNF-alpha) curbed the growth of the bacilli in human macrophages in a reproducible fashion. No cytokine combination was more efficient than TNF-alpha alone. These studies thus highlight the resistance of virulent mycobacteria against different mechanisms of cytokine-induced macrophage bactericidal activity.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.