Marilyn C. Pike

ABNORMALITIES OF LEUKOCYTE CHEMOTAXIS IN HUMAN DISEASE

Dysfunctions of the immune system are associated not only with an increased susceptibility to infection and neoplasia but also with a propensity for the development of systemic inflammatory diseases. The ability of the immune system to function normally is predicated upon its ability to discriminate self from nonself, then to efficiently localize and eliminate material recognized as nonself. The process of localization and elimination of foreign material can be termed an immune-effector function and is largely mediated by an immunologically initiated inflammatory response. The local accumulation of immune effector cells, such as polymorphonuclear leukocytes (PMNs) , macrophages, or lymphocytes, is instrumental in the localization and destruction of “nonself.” PMNs (neutrophils, eosinophils, basophils) and macrophages are wandering phagocytic cells that can migrate unidirectionally along chemical gradients. During the past decade, it has clearly been shown that the interaction of the immune system with antigenic material results in the production of chemotactic factors that attract PMNs and macrophages to sites of immunologic reactions. The development of chemotactic gradients and the ability of wandering cells to respond normally to such gradients appear to be critical to host defense. Dysfunctions of leukocyte migration may therefore render an individual more susceptible to infectious, inflammatory, and perhaps neoplastic diseases. The localization of leukocytes at sites of immune reactions is accomplished by a series of interrelated processes initiated by thc recognition of foreign or neoplastically transformed materials as nonself. The combination of host recognition factors, such as serum immunoglobulins or lymphocytes, with antigens can result in the production or release of biologically active products that enhance vascular permeability, cause local vascular stasis, and attract circulating tissue leukocytes (TABLE 1 ) . The factors that control the magnitude of the inflammatory response are complex and poorly understood but depend in part on the efficiency of the mobilization of inflammatory cells and on the amount of antigenic material present and its “digestability” by PMNs or macrophages. It should be empha-

Transductional mechanisms of chemoattractant receptors on leukocytes.

Phagocytic leukocytes contain receptors for chemoattractants on their cell surface. Binding of chemotactic factors to these receptors initiates a number of coordinated cellular responses in a strict dose-dependent manner. Motility-related functions such as shape change, cytoskeletal rearrangement, and chemotaxis are stimulated by relatively low doses of chemoattractants, while microbiocidal or cytotoxic functions (i.e., secretion of lysosomal enzymes or stimulation of the respiratory burst), require approximately 10- to 50-fold higher concentrations of these agents. The receptor for oligopeptide chemotactic factors on leukocytes has provided an important model for the study of stimulus-response coupling in phagocytic cells. This receptor on human polymorphonuclear leukocytes exists in two affinity states that are partially interconvertible. Guanine nucleotides regulate the convertibility between a portion of the high- and low-affinity states, thereby suggesting that a nucleotide regulatory protein allosterically modifies receptor affinity and participates in its transduction mechanisms. A fraction of the high-affinity receptors in PMN membranes is not subject to guanine nucleotide regulation and appears to be formed by prior exposure of the receptors to specific agonists. This high-affinity form of the oligopeptide chemoattractant receptor is rapidly internalized at 37 degrees C, and its formation may be dependent on aggregation or covalent modification of the receptor. The chemotaxis and microbiocidal functions of PMNs can be divergently manipulated by pharmacological agents indicating that the transduction mechanisms for these two types of processes are independently regulated. Aliphatic alcohols at doses that induce mild fluidization of PMN membranes increase the average affinity of the chemoattractant receptor and enhance chemotactic functions but markedly depress lysosomal enzyme secretion and the respiratory burst. In contrast, polyene antibiotics that bind to membrane cholesterol lower the receptors affinity and depress chemotactic functions but enhance secretion of specific granule enzymes. In addition, transmethylation reactions mediated by S-adenosyl-methionine appear to regulate receptor affinity. When such reactions are blocked pharmacologically, the oligopeptide receptor on macrophages reverts to a lower average affinity form and is ineffective in transducing chemotactic as well as microbicidal functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of transmethylation reactions in cellular motility and phagocytosis

The chemotactic responses of such eukaryotic cells as human polymorphonuclear leukocytes, monocytes and guinea pig macrophages require transmethylation reactions mediated by S-adenosyl methionine. Inhibition of methylation with inhibitors of adenosine deaminase plus adenosine and homocysteine produces as much as a 92% depression of chemotactic responsiveness. While the exact transmethylation reactions required for leukocyte chemotaxis are unknown, alterations of phospholipid methylation appear to be involved. Chemotactic agonists, but not antagonists, depress the methylation of phosphatidylethanolamine in chemotactically responsive cells. Immune phagocytosis, on the other hand, does not depress phospholipid methylation. It is speculated that occupancy of chemotactic factor receptors by chemotactic agonists alters the phospholipid composition, and thus biophysical properties, of newly synthesized membrane at local sites surrounding the receptors. Such asymmetrical alteration of leukocyte membranes may be necessary for sustained polarized locomotion.

Influenza-induced depression of monocyte chemotaxis: Reversal by levamisole☆

Abstract Depression of monocyte chemotactic responsiveness that occurs in patients with acute influenza may be a factor in causing the high incidence of superinfection seen in this viral disease. Levamisole, a pharmacological agent capable of enhancing monocyte chemotaxis, was effective in counteracting the depression of chemotaxis produced by incubating normal monocytes with influenza in vitro . The drug, moreover, enhanced the subnormal in vitro chemotactic responses of monocytes from patients with serologically proven acute influenza. These studies suggest that levamisole may be useful in enhancing depressed cellular immune function in patients with acute influenza.

Influence of cytoskeletal assembly on phosphatidylcholine synthesis in intact phagocytic cells

Interactions of the plasma membrane with the cytoskeleton are required for diverse cellular functions such as adhesion, division, secretion, endocytosis and chemotaxis. We therefore investigated whether the reversible assembly of microtubules and/or microfilaments in leukocytes affected the synthesis of a key membrane component, phosphatidylcholine. The effects of a variety of antitubuin and antimicrofilament agents on phosphatidylcholine synthesis via the methylation of phosphatidyl-ethanolamine and its formation through CDP-choline were studied. The antitubulins inhibited the incorporation of 3H-methyl groups into phosphatidylethanolamine in guinea pig macrophages and polymorphonuclear leukocytes by as much as 64%, while cytochalasin B, an antimicrofilament agent, had no effect. In contrast, the incorporation of methyl-3H-choline into phosphatidylcholine was stimulated in these cells by as much as 2 fold by the anti-tubulins. The synthesis of phosphatidylcholine in a nonphagocytic cell type, splenic lymphocytes, was not altered in the presence of the antitubulin agents. Changes in the state of polymerization of cellular tubulin pools associated with certain specialized functions of cells may, through effects on phosphatidylcholine synthesis, alter local membrane composition, microviscosity, or the interaction of membrane proteins with their environment.

[22] Leukocyte chemoattractant receptors

Publisher Summary This chapter describes various leukocyte chemo-attractant receptors. The accumulation of inflammatory cells is vital for many immunologically mediated functions as well as for wound healing. The receptors have been found on the various types of normal cells, including human, rabbit, and equine polymorphonuclear lymphocytes (PMNs), human monocytes, guinea pig macrophages as well as a variety of differentiated human leukemic cell lines, such as HL60 and U937 .Binding to both intact cells and isolated membranes is demonstrated for some of these cell types. This chapter provides methodology for measuring chemo-attractant receptors on the various types of cells and membranes. The incubation conditions for the quantification of the various chemo-attractant receptors vary and are dealt with individually. The measurement of bound and free ligand can be performed using several separation techniques. A method for quantifying oligopeptide chemo-attractant receptors without the physical separation of bound and free ligand is also discussed.

Disorders of leukocyte chemotaxis.

The rapid accumulation of inflammatory cells at sites of microbial invasion or neoplastic transformation is a central event in immunologically-mediated host defense. The availability of methodology to accurately quantify leukocyte migration in vitro has allowed the disclosure of previously unrecognized clinical disorders, namely leukocyte dysmotility syndromes. Although this area of clinical investigation is in its infancy, one can identify several processes associated with abnormal leukocyte accumulation. Abnormalities of immune recognition, chemotactic factor production, cellular motility or inhibitors of chemotaxis have been identified in different human diseases. In the upcoming years, pharmacological intervention directed at correcting specific causes of leukocyte dysmotility may well enhance our ability to treat certain infectious, inflammatory, and neoplastic diseases.

BIOLOGICAL ACTIVITIES OF A MACROPHAGE CHEMOTAXIS INHIBITOR (MCI) PRODUCED BY NEOPLASMS

Publisher Summary This chapter describes a study to investigate the biological activities of a macrophage chemotaxis inhibitor (MCI) produced by neoplasms. In the study, the MCI was prepared by washing and then sonicating Hepatoma 129 cells. The cell-free supernatant obtained by centrifugation was passed through an Amicon CF25 cone, a membrane designed to exclude molecules above approximately 25,000 daltons. The material that passed through the cones was diluted and injected subcutaneously into the thighs of groups of four mice. Twenty-four hours following the MCI injection, the mice were given intraperitoneal injections of one of the three inflammatory stimulants: (1) phytohemagglutinin (PHA), (2) concanavalin A (Con A), or proteose peptone. Both PHA and Con A are not chemotactic in vitro but activate lymphocytes and generate chemotactic lymphokines. Proteose peptone, on the other hand, is itself chemotactic in vitro. Forty-eight or 72 hours later, the mice were sacrificed, the peritoneal cavities were lavaged, and the total and differential cell counts for the individual peritoneal exudates were determined. The findings demonstrated that the MCI from even small numbers of tumor cells can depress macrophage accumulation to inflammatory agents regardless of whether they are directly chemotactic or stimulate lymphokine production.

REQUIREMENT OF TRANSMETHYLATION REACTIONS FOR EUKARYOTIC CELL CHEMOTAXIS

ABSTRACT Transmethylation reactions mediated by S-adenosyl methionine are required for the chemotactic response of at least two types of eukaryotic cells, human monocytes and guinea pig macrophages. While the transmethylation reaction (s) required for eukaryotic cell chemotaxis are as yet unknown, incubation of chemotactic agents with the cell types studied did not produce a measurable stimulation of carboxy-O-methylation. Phospholipid methylation was, however, depressed by chemotactic factors in intact chemotactically responsive cells. It is suggested that polarized depression of phospholipid methylation occurs when responsive cells sense chemotactic gradients. Local alterations of the composition of methylated phospholipid near sites of occupied chemotactic factor receptors may be necessary for the directed migratory response of eukaryotic cells.

Mechanisms of Nonspecific Host Resistance

A major function of the immune system is the maintenance of the complex biochemical integrity of the host through protection against the penetration and/or the dissemination of biologically active environmental antigens such as microbial agents. The immune system also may play an important role in surveillance against the development and spread of cancer. In order to perform its functions, the immune system must recognize foreign materials and then efficiently eliminate the antigenic substances (Fig. 1). The actual elimination of antigenic material is accomplished by specialized effector cells of the immune system termed “phagocytes.” These cells include polymorphonuclear leukocytes and fixed and wandering mononuclear phagocytes. The recognition of antigens by immunoglobulins and lymphocytes is specific in that these immune components can discriminate subtle differences among antigens. Recognition of antigen by phagocytes is, in general, far less specific. Phagocytes by themselves discriminate only self from nonself and not differences in various forms of nonself. Antigens which enter the circulation are normally removed by the fixed phagocytic cells of the reticuloendothelial system. In other areas of the body however, antigens must be eliminated by phagocytic wandering cells which migrate to an inflammatory focus.