Alfred I. Tauber

Evidence for a protective role of pulmonary surfactant protein D (SP-D) against influenza A viruses.

We tested the hypothesis that pulmonary surfactant-associated lectins--surfactant proteins A and D (SP-A, and -D)--contribute to initial protective mechanisms against influenza A viruses (IAVs). SP-D potently inhibited hemagglutination activity of several strains of IAV as well as causing viral aggregation. SP-D enhanced neutrophil binding of IAV and neutrophil respiratory burst responses to the virus. Neutrophil dysfunction resulting from IAV exposure was diminished when the virus was pre-incubated with SP-D. Each of these effects was mediated by the calcium-dependent carbohydrate-binding property of SP-D. Native SP-D preparations of both human and rat origin, as well as recombinant rat SP-D, had similar activity. SP-A also inhibited IAV hemagglutination activity. We have previously reported that related mammalian serum lectins (mannose-binding lectin [MBL] and conglutinin) have similar effects. SP-D was at least 10-fold more potent at causing hemagglutination inhibition than were SP-A or MBL. SP-D was shown to contribute to potent anti-IAV activity of human bronchoalveolar lavage fluid. These results suggest that SP-D--alone, and in conjunction with SP-A and phagocytic cells--constitutes an important component of the natural immune response to IAV infection within the respiratory tract.

A symbiotic view of life: we have never been individuals.

The notion of the “biological individual” is crucial to studies of genetics, immunology, evolution, development, anatomy, and physiology. Each of these biological subdisciplines has a specific conception of individuality, which has historically provided conceptual contexts for integrating newly acquired data. During the past decade, nucleic acid analysis, especially genomic sequencing and high-throughput RNA techniques, has challenged each of these disciplinary definitions by finding significant interactions of animals and plants with symbiotic microorganisms that disrupt the boundaries that heretofore had characterized the biological individual. Animals cannot be considered individuals by anatomical or physiological criteria because a diversity of symbionts are both present and functional in completing metabolic pathways and serving other physiological functions. Similarly, these new studies have shown that animal development is incomplete without symbionts. Symbionts also constitute a second mode of genetic inheritance, providing selectable genetic variation for natural selection. The immune system also develops, in part, in dialogue with symbionts and thereby functions as a mechanism for integrating microbes into the animal-cell community. Recognizing the “holobiont”—the multicellular eukaryote plus its colonies of persistent symbionts—as a critically important unit of anatomy, development, physiology, immunology, and evolution opens up new investigative avenues and conceptually challenges the ways in which the biological subdisciplines have heretofore characterized living entities.

Chronic granulomatous disease: a syndrome of phagocyte oxidase deficiencies.

Chronic granulomatous disease (CGD) is an inherited disorder of host defense due to the inability of the phagocyte to generate toxic oxygen metabolites upon appropriate stimulation. The disorder is heterogeneous even within the confines of a defective respiratory burst oxidase function, and may arise from a biochemical lesion at either the receptor, the activating pathways or the enzyme level. The identification of defects in plasma membrane depolarization, missing cytochrome and abnormal enzymatic function has yielded new insights into the pathophysiologic basis of CGD. A classification of this syndrome based on more precise biochemical criteria is proposed, which defines the disease as distinct from other associated enzymopathies with similar pathology and emphasizes the metabolic basis of the pathophysiologic defect in phagocyte function. Review of the clinical manifestations, pathogenic organisms and natural course of the disease, emphasizes the critical role of the oxidative metabolism of the normal neutrophil and offers a perspective on oxygen free radical biochemistry in the inflammatory response.

Evidence for hydroxyl radical production by human neutrophils.

The possibility that neutrophils produce the hydroxyl radical (OH-) was studied by examining the ability of these cells to support the release of ethylene from methional, a reaction in which it has been shown that OH-, but not O2- or H2O2, may serve as the oxidizing agent. When neutrophils were exposed to opsonized zymosan in the presence of 0.35 mM methional, ethylene was released in quantities amounting to 44.6+/-3.6 pmol/10(6) cells/40 min. Ethylene production required the presence of neutrophils, opsonized zymosan, and methional, indicating that it was formed from methional by stimulated but not resting neutrophils. Ethylene was not produced by zymosan-treated cells from patients with chronic granulomatous disease, confirming the requirement for respiratory burst activity in this process. Ethylene production was suppressed by benzoic acid, an OH- scavenger. Superoxide dismutase (3 microgram/ml) reduced ethylene production to 21% of control levels, but catalase had no significant effect in this system. These findings indicate that stimulated neutrophils produce a highly reactive oxidizing radical, possibly OH-, which releases ethylene from methional, and that the O2-generated during the respiratory burst is involved in the production of this reactive species.

The immune self: theory or metaphor?

Immunology is one of the unique products of the darwinian age--born in the controversies of that fresh announcement that all species, including ourselves, were not static entities, but subject to change as a result of the vicissitudes of time and circumstance. Darwinism postulated an everchanging species defined by evolutionary necessity. In this scheme, the organism is not given, but evolves. Always adapting, it is always changing. Thus, this raises the core issue of organismal identity as a problem. Here, Alfred Tauber explores the concept of self and traces the development of the term from Metchnikoffs theory that immunity resides in the active pursuit of identity.

Human mannose-binding protein functions as an opsonin for influenza A viruses.

Influenza A viruses (IAVs) cause substantial morbidity and mortality in yearly epidemics, which result from the ability of the virus to alter the antigenicity of its envelope proteins. Despite the rapid replication of this virus and its ability to infect a wide variety of cell types, viremia is rare and the infection is generally limited to the upper respiratory tract. The preimmune host defense response against IAV is generally, therefore, successful. We have previously provided (and summarized) evidence that neutrophils contribute to defense against IAV, although neutrophil dysfunction and local tissue damage may be less salutory byproducts of this response. Here we provide evidence that the serum lectin mannose-binding protein directly inhibits hemagglutinin activity and infectivity of several strains of IAV. In addition mannose-binding protein acts as an opsonin, enhancing neutrophil reactivity against IAV. Opsonization of IAV by mannose-binding protein also protects the neutrophil from IAV-induced dysfunction. These effects are observed with physiologically relevant concentrations of mannose-binding protein. Two different allelic forms of recombinant mannose-binding protein are found to have similar effects. We believe, on the basis of these data, that mannose-binding protein alone and in conjunction with phagocytic cells is an important constituent of natural immunity (i.e., preimmune defense) against IAV.

Activation of the human neutrophil nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase by protein kinase C.

A variety of phagocytosable and soluble agonists stimulate the human neutrophil respiratory burst enzyme, NADPH-oxidase, an activity required for normal microbicidal function. Of these agonists, the phorbol esters, which stimulate diverse systems by their ability to substitute for diacylglycerol to activate protein kinase C (the major phorbol ester receptor), have now been shown to directly stimulate NADPH-oxidase through this same receptor. Almost 90% of the specific receptors for phorbol 12,13-dibutyrate (PDBu) were found in the cytosol upon subcellular fractionation. The dissociation constant for [3H]PDBu was 1.2 nM. No significant difference was found in the distribution of the receptor between subcellular fractions from resting as compared with phorbol 12-myristate 13-acetate (PMA)-stimulated neutrophils. On the basis of these binding studies, we were able to establish a reconstituted system in which PMA activated dormant NADPH-oxidase in a light membrane fraction when cytosol, NADPH, phosphatidylserine, or phosphatidylinositol and ATP were added. The calcium chelator, EGTA, inhibited the activation, which suggested a requirement for calcium at low concentrations. The half-maximally effective PMA dose was 1.1 nM, as predicted from the receptor content in these preparations. Reconstitution of oxidase activity was rapid, peaking within 1 min of incubation. Purified protein kinase C was able to substitute for the cytosol fraction, and accounted for 80% of the cytosol activity. These studies demonstrate that phorbol esters stimulate the neutrophil respiratory burst through activation of cytosolic protein kinase C, which in turn activates either a regulatory constituent or the NADPH-oxidase directly in the plasma membrane to generate an active O-2-generating system.

Novel effects of 1-0-hexadecyl-2-acyl-sn-glycero-3-phosphorylcholine mediators on human leukocyte function: Delineation of the specific roles of the acyl substituents

Abstract Analogues of 1-0-hexadecyl-2-acyl-sn-glycero-3-phosphorylcholine with different 2-acyl substituents are chemotactic for human neutrophils and mononuclear leukocytes and influence other leukocyte functions. The double bond of the 2-maleyl-analogue results in increased chemotactic potency and a free carboxyl-group endows the 2-maleyl- and 2-succinyl-analogues with the capacity to increase neutrophil adherence, while only the 2-acetyl-analogue exhibits secretagogue activity for lysosomal enzymes. Each of the analogues profoundly alters the responsiveness of neutrophils to other chemotactic stimuli without affecting random migration. The distinct profile of functions of each analogue suggests that studies of this new class of leukotactic mediators may contribute to the elucidation of the mechanisms of leukocyte activation.

Proton secretion by stimulated neutrophils. Significance of hexose monophosphate shunt activity as source of electrons and protons for the respiratory burst.

Phagocytosis by neutrophils is accompanied by a burst in O2 consumption and activation of the hexose monophosphate shunt (HMPS). Proton secretion equal to the amount of O2 consumed is an additional feature of the respiratory burst, but its source has not been identified, nor has the source of all electrons donated to O2 in the respiratory burst. We chemically quantitated total CO2 generation in human neutrophils and found that proton secretion elicited by phagocytosis was accompanied by a stoichiometric increase in CO2 generation. Addition of carbonic anhydrase and its inhibitors had no effect on either the quantities of CO2 measured or the quantities of protons secreted. Therefore, the CO2 generated in the respiratory burst of stimulated neutrophils is hydrated to form H2CO3, which then dissociates, accounting for the observed proton secretion. Furthermore, the CO2 generated corresponds to the O2 consumed with a respiratory quotient of nearly 1. We conclude on the basis of this and previous studies that the HMPS activity is the source of both the electrons for the NADPH oxidase and of protons secreted in association with the respiratory burst.

Specific binding of haptoglobin to human neutrophils and its functional consequences.

Haptoglobin, an acute phase reactant protein, has been shown to modulate various facets of immune responses. In this paper we examined the effect of haptoglobin on human neutrophils at the molecular level. First, we found that native haptoglobin binds at two distinct sites on neutrophils. We then examined the effects of this binding at normal and pathophysiological concentrations of haptoglobin found in human serum. Of the various functional parameters assessed, neutrophil respiratory burst activity, as assessed by superoxide (O2‐) production, was inhibited by native haptoglobin when the cells were stimulated with formylmethlonyl‐leucylphenylalanine (FMLP), arachidonic acid (AA), and opsonized zymosan. The rise in intracellular calcium induced by FMLP stimulation was also inhibited by native haptoglobin. Since the generation of O2‐ was unaffected by native haptoglobin in phorbol myristate acetate (PMA)‐stimulated neutrophils, the likely site of haptoglobin inhibition on neutrophil function is at a point of receptor‐ligand interaction in the activation cascade. The role of haptoglobin as a modifier of the immune response has here been extended to altered neutrophil function stimulated by diverse agonists.