Monte S. Meltzer

Cytokine-induced synthesis of nitrogen oxides in macrophages: a protective host response to Leishmania and other intracellular pathogens.

Fixed macrophages within tissues and the mononuclear phagocytes cabled to sites of inflammation are premier scavenger cells able to eliminate most infectious threats by a wide array of toxic effector molecules and hydrolytic enzymes. Paradoxically, a variety of protozoa, bacteria, fungi, and viruses preferentially infect and replicate within these same scavenger cells. Sites of replication include not only the phagobysosome, but also the cytoplasm of infected cells. In many instances, these microorganisms can also be killed by the infected macrophage host cell. Complex signals generated through the cytokine network of local and systemic immune reactions induce a state of activation in the infected cell which kills the intracellular parasite (presumably without killing the infected macrophage). Effector molecules that such activated macrophages use to kill and eliminate these pathogens have always been a mystery. In this review, we examine the experimental approaches that identified nitrogen oxides derived from L-arginine as essential components in the microbicidab activity of cytokineactivated macrophages, and discuss the fascinating, but complex interactions of host cells, cytokines, and infectious pathogens that regulate production and action of toxic nitrogen oxides. Details of the biochemical pathways for nitrogen oxidation of L-arginine and its regulation within mammabian cells are now emerging [1-3]. Although not fully characterized, it is known that nitric oxide (NO) is a short-lived intermediate product of this novel pathway

Cellular mechanisms of nonspecific immunity to intracellular infection: Cytokine-induced synthesis of toxic nitrogen oxides from l-arginine by macrophages and hepatocytes

Nitric oxide (NO) produced by cytokine-treated macrophages and hepatocytes plays a vital role in protective host responses to infectious pathogens. NO inhibits iron-sulfur-dependent enzymes involved in cellular respiration, energy production, and reproduction. Synthesis of L-arginine-derived nitrite (NO2-), the oxidative end product of NO, directly correlates with intracellular killing of Leishmania major, an obligate intracellular protozoan parasite of macrophages: the level of NO2- production is a quantitative index for macrophage activation. The competitive inhibitor of NO synthesis, monomethylarginine (NGMMLA), inhibits both parasite killing and NO2- production. For Leishmania, the parasite itself participates in the regulation of this toxic effector mechanism. This participation is mediated by parasite induction of tumor necrosis factor alpha (TNF alpha), an autocrine factor of macrophages: NO synthesis by interferon-gamma (IFN-gamma)-treated cells can be blocked by monoclonal antibodies to TNF alpha. NO production by IFN gamma-treated hepatocytes is of special interest in malaria infections: sporozoite-infected hepatocytes kill the intracellular malaria parasite after treatment with IFN gamma; this killing is inhibited by NGMMLA.

Colony-stimulating factors

Recombinant hematopoietic colony-stimulating factors have profound effects on developing and mature granulocytes, macrophages, and lymphocytes. Use of these agents for treatment of disease may result in a variety of adverse cutaneous reactions. The recent discovery of colony-stimulating factor production by keratinocytes and dermal cells suggests that these agents may also be significant in cutaneous homeostasis and in the pathogenesis of cutaneous diseases.

Macrophages and the human immunodeficiency virus

Abstract Mononuclear phagocytes are major participants in human immunodeficiency virus (HIV) disease. These cells function as susceptible targets, persistent reservoirs for virus in tissue and key immunoregulatory elements that control the level of virus replication and the extent of disease. In this review, the second of the series, Monte Meltzer and colleagues review the distinct interactions between HIV and monocytes and between HIV and T cells. Understanding this dualism may more clearly define both the pathogenesis of HIV disease and strategies for therapeutic intervention.

Tumoricidal responses in vitro of peritoneal macrophages from conventionally housed and germ-free nude mice

Abstract Peritoneal macrophages from untreated nude mice were nonspecifically cytotoxic to tumor cells in vitro and were more responsive to chemotactic stimuli than macrophages from normal mice or from phenotypically normal littermates of nude mice. Tumoricidal and chemotactic responses of activated macrophages from nude mice were quantitatively comparable to responses of macrophages from BCG-infected normal mice. Peritoneal macrophages from germ-free nude mice, however, were not tumoricidal in vitro . These observations suggest that environmental stimuli, rather than thymic deficiency per se, induced activated macrophages in nude mice.

Interaction of BCG-activated macrophages with neoplastic and nonneoplastic cell lines in vitro: Cinemicrographic analysis

Cultures of adherent peritoneal cells (macrophages) from bacillus Calmette-Guerin (BCG)-infected (BCG macrophages) or from uninfected mice with neoplastic or nonneoplastic target cells were filmed by time-lapse cinemicroscopy. A single film of each of the macrophage-target cell combinations was analyzed in detail. This analysis revealed dramatic changes in both effector and target cell populations. The translational movement of BCG macrophages on tumor cells was up to 5 times the movement observed on nonneoplastic target cells. This effect was not observed with macrophages from uninfected mice. Bacillus Calmette-Guerin macrophage-tumor cell interaction was characterized by repeated and relatively short (2-hr) contacts inducing complete and permanent tumor cytostasis, degenerative morphological changes, and eventual destruction of the tumor monolayer. Bacillus Calmette-Guerin macrophages were partially cytostatic to nonneoplastic target cells, but degenerative changes or target cell death were not observed. Macrophages from uninfected mice had little or no effect on either target cell line.

Tumor necrosis factor

Tumor necrosis factor is important in systemic and cutaneous defense, homeostasis, and many disease states. The numerous and diverse effects of tumor necrosis factor are best understood when considered as concentration-dependent, with normal homeostasis progressing to defense followed by toxic effects. Understanding tumor necrosis factor is important for the dermatologist as more studies appear in our literature and potential clinical uses of tumor necrosis factor (and possible anti-tumor necrosis factor agents) are realized.

Macrophage activation for tumor cytotoxicity: Tumoricidal activity by macrophages from C3H/HeJ mice requires at least two activation stimuli

Macrophages from C3H/HeN mice treated in vivo with Mycobacterium bovis, strain BCG or in vitro with supernatants from antigen-stimulated leukocyte cultures (lymphokines) were cytotoxic to tumor cells in vitro. Macrophage tumoricidal activity, however, did not develop after identical in vivo or in vitro treatment of cells from endotoxin (LPS)-unresponsive C3H/HeJ mice. Increasing time of macrophage incubation in lymphokines, concentration of lymphokines or number of lymphokine-treated macrophages added to tumor cells did not evoke tumoricidal activity. Similarly, varying time of macrophage collection after BCG infection, numbers of BCG organisms in the infectious inoculum or numbers of macrophages from BCG-infected mice added to tumor cells also did not evoke cytotoxic activity. The tumorical defect of macrophages from C3H/HeJ mice appeared highly selective: inflammatory responses to BCG infection in C3H/HeN and C3H/HeJ mice were indistinguishable; moreover, no difference was detected between these strains in production of macrophage activation factors. Thus, despite normal inflammatory reactions, normal production of lymphokines and extensive experimental manipulation of single activation stimuli, macrophages from C3H/HeJ mice did not express tumoricidal activity in vitro. Nevertheless, macrophages from C3H/HeJ mice could develop tumoricidal activity under appropriate conditions. Macrophages from in vivo immune reactions (BCG infection, Con A injection), but not from irritant-induced peritoneal exudates, developed full cytotoxic activity after exposure to certain in vitro stimuli. These stimuli include microgram/ml concentrations of LPS and certain factors in lymphokine supernatants or supernatants from a T-cell lymphoma line. The effect of LPS but not that of lymphokines or lymphoma culture supernatants was abrogated by polymyxin B. These data suggest that the ultimate expression of macrophage cytotoxicity may depend upon certain signals from the milieu of immune reactions. These expression signals, derived from bacterial organisms or from soluble mediators of immune responses, provide the necessary and final stimulus for macrophage activation. The tumoricidal defect of macrophages from C3H/HeJ mice reflects a genetic inability of these cells to respond to environmental expression signals.

T-cell-mediated activation of macrophages

Functionally diverse subpopulations of macrophages and lymphocytes, a wide array of stimulatory signals, and an enormous effector repertoire of activated macrophages keeps this field dynamically active. We review new advances in the identification of cytokines that interact to activate macrophages, and in the discovery of effector molecules used by activated macrophages to destroy their targets.

Macrophage - HIV interaction: Viral isolation and target cell tropism

Viral isolates were recovered by cocultivation on macrophage colony-stimulatingfactor (MCSF)-treated monocyte target cells from peripheral blood mononuclear cells (PBMCs) in 25 out of 27 patients seropositive or at risk for HIV infection. Frequency of virus recovery was independent of the patients age, sex, numbers of CD4+ T cells, clinical stage or zidovudine (azidothymidine) therapy. Sixteen out of 19 HIV isolates were serially passaged in MCSF- treated monocytes. Five out of five virus isolates were also passaged in phytohemagglutinin/interleukin-2 (PHA/IL-2)-treated lymphoblasts. In lymphoblasts, no qualitative or quantitative differences were observed between these isolates and human T-cell leukemia virus IIIB (HTLV-IIIB) for (1) release of p24 antigen reverse transcriptase, and infectious virus, (2) induction of typical cytopathic effects (cell syncytia in 3–10% of cells) and cell lysis, (3) frequency of infected cells (5–20% of PBMC) as detected by in situ hybridization for HIV RNA, (4) down-modulation of T cell plasma membrane CD4, and (5) site of progeny virion assembly and budding (plasma membrane only with no intracytoplasmic accumulation of virus). Progeny virus recovered from infected lymphoblasts was fully infectious for other lymphoblasts, but failed to infect MCSF-treated monocytes. Detailed analysis of target cell tropism among HIV isolates showed that HIV isolated in monocytes infected both monocytes and lymphoblasts; progeny virus isolated in lymphoblasts infected only T cells. HIV interacts differently with monocytes and T cells. Understanding this interaction may more clearly define both the pathogenesis of HIV disease and strategies for therapeutic intervention.