Chemotactic Factor Inactivator Research Articles

Inactivation of Chemotactic Factor Inactivator by Cigarette Smoke: A Potential Mechanism of Modulating Neutrophil Recruitment to the Lung

Activation of the complement system with generation of the potent neutrophil chemotactic factor C5a has been proposed to play a significant role in the neutrophil accumulation in the lungs of cigarette smokers. Chemotactic factor inactivator (CFI) can inhibit C5a-directed neutrophil chemotaxis by binding to the C5a cochemotaxin GcGlobulin (GcG), a vitamin-D-binding protein, and inhibiting the capacity of GcG to enhance the chemotactic activity of C5a. Because cigarette smoke can inhibit the function of some proteins, a loss of CFI functional activity induced by cigarette smoke would allow an increased capacity of GcG to augment C5a-directed neutrophil chemotaxis. In order to test this hypothesis, cigarette smoke was bubbled through a CFI solution, and the solution was evaluated for its ability to inhibit the chemotactic activity of C5a and GcG. Smoke-treated CFI inhibited only 36% of the C5a-GcG chemotactic activity. In contrast, a CFI solution treated with air inhibited 62% of the chemotactic activity (p less than 0.001). Consistent with these observations, smoke-treated CFI exhibited a decreased capacity to bind to GcG and a decreased capacity to inhibit the binding of C5a des Arg to GcG. CFI contained in the bronchial lavage fluids obtained from patients with chronic obstructive pulmonary disease secondary to cigarette smoking and asymptomatic smokers exhibited a decreased capacity to inhibit C5a-GcG neutrophil chemotaxis and to bind to GcG (p less than 0.05, both comparisons). Furthermore, smoke bubbled through normal bronchial lavage fluid decreased the capacity of CFI to bind to GcG.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional Loss of Chemotactic Factor Inactivator in the Adult Respiratory Distress Syndrome

The adult respiratory distress syndrome (ARDS) is often characterized by a neutrophilic alveolitis, which may be mediated in part by the neutrophil chemoattractant, C5a. Chemotactic factor inactivator (CFI) can decrease C5a-directed neutrophil chemotaxis. Thus, a loss of CFI activity in the ARDS lung could lead to an increased ability of C5a to attract neutrophils. Lung CFI levels were measured antigenically and functionally in bronchoalveolar lavage (BAL) fluid obtained from 29 patients with ARDS and in 14 normal control subjects. Antigenic levels of CFI were found to be markedly elevated in ARDS BAL fluid (1,855 +/- 437 ng/ml) compared with that in normal BAL (29 +/- 10 ng/ml, p less than 0.005), but, in contrast, CFI functional activity was markedly decreased in ARDS BAL fluid compared with that in normal BAL fluid (31 +/- 7% inhibition versus 76 +/- 5% inhibition, p less than 0.01). Furthermore, although purified CFI readily inhibited the ability of C5a to attract neutrophils (92% inhibition), this activity was decreased when BAL fluid from patients with ARDS was incubated with CFI (47 +/- 10%, p less than 0.01). These findings suggest that patients with ARDS are functionally deficient in CFI, leading to an increased ability of C5a to attract neutrophils.

21] Inhibitors of chemotaxis

This chapter focuses on the inhibition of chemotaxis. There are two relatively well-defined chemotactic factor-directed inhibitors. Both are irreversible inhibitors of their target chemotactic attractant and thus are called inactivators: the anaphylatoxin inactivator and the chemotactic factor inactivator. As with all cell responses, neutrophil chemotaxis requires regulation to participate in an effective and controlled host response. In the absence of strictly regulated chemotactic responses, uncontrolled inflammation would result. Natural inhibitors of chemotaxis are to be expected and are indeed present. Because there are two participants in the chemotactic response, the chemotactic signal and the responding cell, inhibitors may be best classified according to their specific target––that is, inhibitors of chemotactic factors and cell-directed inhibitors. There are three relatively well-defined inhibitors, two of which have chemotactic factors for their target and one of which acts directly to inhibit the responding cells. The chapter discusses these three groups of inhibitors.

Purification and characteristics of the streptococcal chemotactic factor inactivator.

The biochemical and immunological characteristics of the chemotactic factor inactivator of group A streptococci (SCFI) were examined. SCFI was extracted from intact M+ bacteria by limited trypsin digestion and purified sequentially by ammonium sulfate fractionation, hydrophobic interaction chromatography, and anion-exchange chromatography. SCFI activity was associated with multiple species as indicated by gel permeation chromatography and DEAE high-pressure liquid chromatography analyses. Polyacrylamide gel electrophoresis of the column-purified protein also demonstrated a high degree of molecular heterogeneity, with most of the material in a 103,000 to 114,000 Mr cluster. SCFI activity was sensitive to destruction by several proteolytic enzymes, and polyclonal antiserum to SCFI was able to neutralize its antichemotactic activity. Two-dimensional immunoelectrophoresis of SCFI indicated that the various copurified species were immunologically cross-reactive and indicated a high degree of antigenic homogeneity within the preparation. Western blot analysis of crude detergent extracts of M+ bacteria identified a major antigenic species corresponding to 135,000 Mr and a less abundant species of 137,000 Mr. SCFI antiserum was not reactive with M protein, and therefore SCFI appeared to be a distinct molecule, despite its close association with the M+ phenotype.

Mechanism of action of the group A streptococcal C5a inactivator.

Virulent group A streptococci have been found to express a cell-surface factor that has the capability of inactivating complement-derived chemotactic factors. To determine the mechanism of action of this factor, we examined the interaction of purified inactivator with pure C5a chemotaxin. Ligand-receptor binding studies demonstrated that streptococcal chemotactic factor inactivator (SCFI)-treated C5a expressed a greatly reduced ability to bind to receptors of polymorphonuclear leukocytes as compared with native C5a. The inactivation of C5a occurred by a nonstoichiometric and temperature-dependent process. NaDodSO4/PAGE analysis indicated that SCFI mediated a small decrease in the molecular weight of C5adesArg, and sequencing of the carboxyl terminus of inactivated C5a demonstrated that a six-residue peptide was lost. The release of discrete peptide fragments from denatured bovine serum albumin upon prolonged incubation with SCFI was indicative of endoprotease activity. Although denatured bovine serum albumin was inefficiently cleaved, native bovine serum albumin and other native proteins were highly resistant to SCFI proteolysis; this indicated that activity was specific in nature.

Human neutrophil chemotactic response to group A streptococci: bacteria-mediated interference with complement-derived chemotactic factors.

The influence of M protein on the capacity of group A streptococci to generate neutrophil chemotactic activity in normal human serum was examined. Incubation of serum with M- bacteria for up to 10 min led to the production of chemotactic activity. In contrast, incubation of serum with M+ bacteria did not elicit serum chemotactic activity over a 1-h period, even though complement was activated to completion. Further experiments revealed that both M+ and M- bacteria could inhibit the chemotactic activity of serum preexposed to zymosan. However, the M+ bacteria possessed a 130-fold-greater inhibitory capacity in this regard than the M- bacteria. This antichemotactic property was not detectable in the fluid phase of serum incubated with bacteria, thereby ruling out neutrophil-directed effects. Treatment of the bacteria with trypsin resulted in the release of the inhibitory molecule, suggesting that proteins are involved in its maintenance at the cell surface. However, the resistance of the chemotactic factor inactivator to pepsin and trypsin indicated that the protease-sensitive M protein was not involved. These results demonstrate a heretofore uncharacterized activity of group A streptococci that may contribute to virulence through modulation of the host chemotactic response.

Influence of serum on impaired neutrophil chemotaxis after thermal injury

Impaired neutrophil chemotaxis has been consistently documented after thermal injury but whether this defect is primarily related to an acquired cellular defect or to humoral factors is not clear. To study this question, serial neutrophil chemotaxis measurements using the agarose technique of chemotaxis, were made in 34 patients with a mean burn size of 33%. Eighty-three percent of these patients developed a neutrophil chemotactic defect at some time during their hospital stay. The results of this study indicated that the serum from burn patients did not contain cell-directed inhibitor(s) of chemotaxis (CDI) or chemotactic factor inactivator(s). Furthermore, the chemotactic defect in the burn patient's neutrophils could not be reversed by normal human serum, suggesting that the cause of this defect was not related to the absence of normal circulating humoral substances. Additionally, no suppressive effect of silvadene (10 g/ml) on neutrophil chemotaxis was found. Therefore, we concluded that stable serum factors were not likely to play a major role in the development of the acquired neutrophil defect thermal injury.

Development of chemotactic factor inactivation - a fetal lamb model.

Summary: To study the developmental pattern of chemotactic factor in-activator (CFI) activity, although avoiding the effects of labor and delivery, serial blood samples were obtained from eight chronically catheterized lamb fetuses, 13 pregnant, and 13 nonpregnant ewes. The biologic profiles of adult sheep neutrophils in response to sheep C5-derived chemotactic fractions (C5-fr) were determined by the chemotactic and lysosomal enzyme release assays. CFI activity in sheep plasma was characterized and measured by the % inhibition of C5-fr-induced neutrophil lysosomal enzyme release. The chemotactic and enzyme release profiles of sheep neutrophils paralleled those of human neutrophils. Sheep plasma was shown to contain a CFI-like activity similar to that in human plasma. Mean CFI activity was higher in the plasma of pregnant ewes as compare to nonpregnant ewes (7.60 versus 5.15%, P < 0.001). Higher CFI levels (39.5%) were shown in the plasma of chronically catheterized fetuses early in the third trimester of pregnancy (109 days gestational age). These fetal levels decreased progressively to attain normal adult levels at fetal maturity (147 days gestational age) and no significant changes were noted at or after birth. Because identical changes occurred in all chronically catheterized fetuses, a developmental pattern was defined for CFI. Control CFI levels from six acutely catheterized fetuses did not differ from those predicted by the developmental pattern. Thus, the changes in CFI activity were not related to the chronic catheterization or to events surrounding labor and delivery; rather CFI levels correlated best with fetal immaturity. CFI levels correlated inversely with ability of zymosan activated plasma to induce neutrophil chemotaxis (r = —0.96, P < 0.01), suggesting that CFI plays a major role in the regulation of leukocytes chemotaxis. These data confirm previous findings in human neonates and provide a model for future studies. Further studies into the biology of the changes in CFI activity in the fetus and the influence of such high risk factors as prematurity, fetal distress or premature rupture of membranes should enhance our understanding of the immunocompromised neonate.

ELEVATION OF SERUM CHEMOTACTIC FACTOR INACTIVATOR ACTIVITY DURING ACUTE INFLAMMATORY REACTIONS IN RABBITS AND HUMANS

Annals of the New York Academy of SciencesVolume 389, Issue 1 p. 451-453 ELEVATION OF SERUM CHEMOTACTIC FACTOR INACTIVATOR ACTIVITY DURING ACUTE INFLAMMATORY REACTIONS IN RABBITS AND HUMANS D. L. Kreutzer, D. L. Kreutzer Departments of Pathology and Medicine University of Connecticut Health Center Farmington, Connecticut 19942Search for more papers by this authorJ. R. Hupp, J. R. Hupp Departments of Pathology and Medicine University of Connecticut Health Center Farmington, Connecticut 19942Search for more papers by this authorJ. R. McCormick, J. R. McCormick Departments of Pathology and Medicine University of Connecticut Health Center Farmington, Connecticut 19942Search for more papers by this author D. L. Kreutzer, D. L. Kreutzer Departments of Pathology and Medicine University of Connecticut Health Center Farmington, Connecticut 19942Search for more papers by this authorJ. R. Hupp, J. R. Hupp Departments of Pathology and Medicine University of Connecticut Health Center Farmington, Connecticut 19942Search for more papers by this authorJ. R. McCormick, J. R. McCormick Departments of Pathology and Medicine University of Connecticut Health Center Farmington, Connecticut 19942Search for more papers by this author First published: June 1982 https://doi.org/10.1111/j.1749-6632.1982.tb22168.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume389, Issue1C‐Reactive Protein and the Plasma Protein Response to Tissue InjuryJune 1982Pages 451-453 RelatedInformation

Elevation of serum chemotactic factor inactivator activity during acute inflammatory reactions in patients with hypersensitivity pneumonitis.

Inflammatory mediators such as the vasoactive and chemotactic factors derived from the activation of the complement system are extremely potent biological peptides that are under rigid control of specific serum-derived regulators, e.g., the anaphylatoxin inactivator (AI) and the chemotactic factor inactivator (CFI). We have previously demonstrated that serum chemotactic factor inactivator concentrations are altered during chronic inflammatory states; here we demonstrate that a rapid elevation of serum CFI activity occurs during acute inflammatory reactions in patients suffering from hypersensitivity pneumonitis. Specifically, serum CFI concentrations were evaluated in patients with hypersensitivity pneumonitis (pigeon breeder's disease) and control subjects (asymptomatic) after aerosol challenge with 2 ml of sterile pigeon serum. At 4 h postchallenge, serum CFI concentrations in the patients with hypersensitivity pneumonitis increased rapidly to 3 times the prechallenge serum concentrations. Asymptomatic (control) subjects showed no increase in serum CFI concentrations after exposure to pigeon serum. In independent studies, we have also demonstrated that serum CFI concentrations are elevated in (1) rabbits with glycogen-induced peritonitis, (2) rabbits after intravenous infusion of C5-derived chemotactic factors, and (3) patients undergoing hemodialysis. These combined data clearly demonstrate that serum CFI activity is rapidly elevated during acute inflammatory reactions within both patient and animal populations, and suggest that serum CFI may represent a "hyperacute" phase reactant that is elevated during inflammation. Possibly, this elevation of CFI may be induced in response to inflammatory mediators produced during inflammation. Thus, the acute elevation of serum CFI concentrations that occurs during acute inflammation may represent the control system that would be responsive to the regulatory needs of the body during inflammatory reactions.

Prognostic significance of abnormal neutrophil chemotaxis after thermal injury.

Neutrophil chemotaxis was studied sequentially in 23 thermally injured patients and 23 normal volunteers. The average age of the burn victims was 48 years (range, 21-87) and mean total body surface area burned was 33% with a mean full-thickness component of 16%. Chemotaxis was measured under agarose since this test system allowed the chemotactic generating ability of the patients' serum to be evaluated as well as the chemotactic capability of the neutrophils. In excess of 800 determinations were performed on the burned patient population. Eighty-three per cent of the patient population had a decrease in chemotaxis two standard deviations below normal at some time during the hospital stay, in most patients three or more days postburn. This chemotactic defect appeared to be unrelated to the presence of a chemotactic factor inactivator. There was no statistically significant correlation between the development of abnormal chemotaxis and sepsis or mortality in this patient population.

Monocyte count, monocyte chemotaxis and chemotactic factor inactivator in gastric cancer patients.

The monocyte count in the peripheral blood, chemotactic responsiveness (MCR) and chemotactic factor inactivator (CFI) were measured in 66 patients with gastric cancer. Monocyte counts in advanced gastric cancer patients were significantly increased. MCR was significantly depressed in gastric cancer patients in the advanced stage of the disease, as compared with findings in the control groups. Sixty-seven percent of the patients with stage IV carcinoma had abnormally depressed responses. The CFIs were significantly higher in gastric cancer patients than in the control groups, and there was a positive correlation between the degree of inhibition and extent of cancer progress. These data support the hypothesis that qualitative and quantitative abnormalities of circulating monocytes, as macrophage precursors, may hinder immunological host defense mechanisms.

Cell-directed inhibitor of human leukocyte locomotion. Identification of immunoglobulin G as a cell-directed inhibitor in normal human serum.

Abstract We purified a CDI of leukocyte locomotion from normal human serum and identified it as IgG. We studied the effect of purified whole IgG, its Fc and Fab fragments, IgA, and IgM on leukocyte locomotion in micropore filters, using measurements of both the distance migrated and the number of cells migrating (mass migration). Based on the distance migrated by the fastest PMNLs, the %I max is 40% ± 13 (mean ± S.D.) for IgG, 46% for the Fc fragment, and 40% for IgA. The inhibitor concentrations producing half-maximal inhibition (K i ) are 0.083 ± 0.053 μM for IgG, 2.4 for the Fc fragment, and 0.042 for IgA. Based on the number of granulocytes migrating into the filters (mass migration response), %I max is 50% ± 10 for IgG, 88% for the Fc fragment, and 72% for IgA. The K i values are 0.051 ± 0.036 μM for IgG, 4.2 for the Fc fragment, and 0.12 for IgA. No effect was observed with the Fab fragment up to a concentration of 33 μM or with IgM up to a concentration of 1.5 μM. The inhibition produced by IgG in the upper compartment of the modified Boyden chamber was not affected by the presence of chemotactic attractant in the lower compartment, indicating that it is an inhibitor of locomotion rather than of the chemotactic response per se and that the observed inhibitory effect of IgG on chemotaxis is actually the result of its effect on locomotion. When IgG was present in the lower compartment with chemotactic factors, neither inhibition nor stimulation was observed. Thus IgG possesses neither chemotactic factor inactivator activity nor chemotactic activity. Consistent with the other previously noted effects of CDI, IgG also inhibits the locomotion of monocytes and decreases the phagocytic responses of both PMNLs and monocytes. Finally, IgG also increases the adherence of neutrophils to nylon fibers. These results indicate that in addition to its other known activities, IgG may be an important regulator of PMNL function. (J Lab Clin Med 98:58, 1981.)

883 DECREASED CHEMOTACTIC ACTIVITY IN NEONATAL PLASMA: ROLE OF CHEMOTACTIC FACTOR INACTIVATOR AND COMPLEMENT LEVELS

Compared to adult plasma, the chemotactic activity of neonatal zymosan activated plasma (ZAP) is decreased. Consequently, we evaluated the role of chemotactic factor inactivator (CFI) and complement levels in this defect. Plasma of 15 neonates and 15 adults were studied. The chemotactic activity of ZAP was measured under agarose, using adult neutrophils as target cells. CFI levels were determined by incubating 0.1 μl plasma with 50 μl C5-derived chemotactic fractions and then measuring the percent decrease in glucosaminidase release from cytochalasin B-treated neutrophils. C3, C5, factor B, properdin and properdin convertase were determined immunochemically; and Cl, C2, C4, C3-9 and CH50 by hemolytic assays in 10 of these infants and adults. Compared to adult plasma, the chemotactic activity induced by infant plasma was decreased (80 ± 7% of control [mean ± SD], vs. 95 ± 3%, p < 0.001), CFI levels were increased (19 ± 6 vs. 7.5 ± 3, p < 0.001), and complement component levels were decreased (p < 0.05), except for C2. The chemotactic activity correlated inversely with CFI levels (r = -0.958, p < 0.001). After adjusting for the effects of CFI, there was no significant correlation between the chemotactic activity and any of the complement components tested. Thus, differences in CFI, rather than in complement levels, accounted for the differences in chemotactic activity between infant and adult plasma.

Interrelationships between Serum Chemotactic Factor Inactivator, Alpha1-Antitrypsin Deficiency, and Chronic Obstructive Lung Disease1–4

Serum chemotactic factor inactivator (CFI) activity was quantitated in 22 subjects with chronic airflow obstruction (CAO); 8 had normal antitrypsin levels (Pi M phenotype), 6 had intermediate antitrypsin deficiency (Pi MZ phenotype), and 8 had severe antitrypsin deficiency (Pi Z phenotype). We studied 19 healthy subjects with normal lung function as controls; 3 had Pi M and 6 had Pi MZ phenotypes. Subjects with CAO, irrespective of the alpha 1-antitrypsin (AAT) phenotype, had significantly lower CFI activity than the normal subjects; the lowest levels were found in those with CAO and Pi Z phenotype. Normal subjects with intermediate AAT deficiency and MZ phenotype had normal levels of CFI. The results suggest that deficiency of serum CFI may be important in the pathogenesis of chronic airflow obstruction, particularly in those with severe AAT deficiency.

Infection in patients with systemic lupus erythematosus. Association with a serum inhibitor of complement-derived chemotactic activity.

We have found subnormal amounts of chemotactic activity in zymosan-treated sera from 13 of 29 patients with systemic lupus erythematosus (SLE). As an explanation for this abnormality, the presence of a uniquely specific, heat-stable inhibitor of complement (C5)-derived chemotactic activity has been documented in sera from 11 of these patients. Sera from 2 other patients contained elevated levels of nonspecific, heat-labile chemotactic factor inactivator (CFI) activity. The serum from 1 patient contained the heat-stable inhibitor as well as elevated levels of CFI. Patients with SLE whose sera contained the heat-stable inhibitor had more active disease clinically, but otherwise they were indistinguishable from patients without the inhibitor. When patients with the heat-stable inhibitor improved clinically, this usually was accompanied by a decrease in serum inhibitory activity. Only one episode of bacterial infection was observed among 16 patients with SLE whose sera yielded normal amounts of chemotactic activity after treatment with zymosan. In contrast, 7 of 11 patients with SLE whose sera contained the heat-stable inhibitor suffered serious bacterial infections. The presence of this heat-stable inhibitor in sera from some patients with SLE may contribute, in part, to their increased susceptibility to infection.

A Chemotactic Inhibitor Produced by Blast Cells and Present in the Serum of a Patient With Acute Lymphoblastic Leukemia

A chemotactic factor inhibitor (CFI) was found in the serum of a patient with acute lymphoblastic leukemia. The factor was characterized as heat-labile, with activity against complement-dependent chemotactic factors and against the chemotactic factor produced by Escherichia coli. Normal sera and sera from other patients with acute leukemia also demonstrate heat-labile inhibitory activity against comple-ment-dependent chemotactic factors but not against the E. coli-derived chemotactic factor. Supernatants from cultured lym-phoblasts of the patient also possessed CFI activity similar in character to that found in his serum. It is suggested that in vivo the lymphoblasts were responsible for the chemotactic defect observed in his serum, presumably by manufacturing and releasing a chemotactic factor inactivator.

A chemotactic inhibitor produced by blast cells and present in the serum of a patient with acute lymphoblastic leukemia

A chemotactic factor inhibitor (CFI) was found in the serum of a patient with acute lymphoblastic leukemia. The factor was characterized as heat-labile, with activity against complement-dependent chemotactic factors and against the chemotactic factor produced by Escherichia coli. Normal sera and sera from other patients with acute leukemia also demonstrate heat-labile inhibitory activity against complement- dependent chemotactic factors but not against the E. coli-derived chemotactic factor. Supernatants from cultured lymphoblasts of the patient also possessed CFI activity similar in character to that found in his serum. It is suggested that in vivo the lymphoblasts were responsible for the chemotactic defect observed in his serum, presumably by manufacturing and releasing a chemotactic factor inactivator.

Chemotactic factor inactivator release from rat leukocytes.

Rat neutrophils, alveolar macrophages, and peritoneal macrophages each released chemotactic factor inactivator (CFI) activities under conditions of endocytosis (uptake of opsonized zymosan particles and preformed immune complexes). CFI activities in supernatant fluids from phagocytizing leukocytes were found for the chemotactic factors from the third (C3) and the fifth (C5) components of complement and for the bacterial chemotactic factor (present in culture supernatant fluids from Escherichia coli.) CFI activity could also be demonstrated in homogenates obtained from disrupted leukocytes. CFI release from intact leukocytes was dependent on the duration of incubation of leukocytes with the phagocytic stimulus. No quantitative relationships were noted between the amount of CFI activity and the amount of beta-glucuronidase in phagocytic supernatant fluids released from leukocytes. The release of CFI activities from phagocytizing leukocytes may represent a regulatory ("turn-off") mechanism for the inflammatory response.

Quantitative comparisons of various biological responses of neutrophils to different active and inactive chemotactic factors

The effects of chemotactic factors on rabbit neutrophils were evaluated measuring cell migration in modified Boyden chambers and under agarose, in lysosomal enzyme release, leukocyte aggregation, and in vivo neutropenia. Chemotactins employed included the complement-derived C3 and C5 fragments, the bacterial chemotactic factor from culture supernatant fluids of Escherichia coli, and the synthetic chemotactic factors Met-Leu-Phe and formyl-Met-Leu-Phe. A consistent parallelism was found in all the leukocyte responses to a given chemotactic factor. In no instance, with any of the five chemotactic factor preparations, did cells responding in one assay system fail to respond in the four other assay systems, suggesting a common event in all of the cell responses. Boyden chamber chemotaxis was consistently the most sensitive assay; the agarose assay was, in general, less sensitive by a factor of 100 fold. Enzyme release approaches, in cell sensitivity to chemotactic factors, that of the Boyden chamber assay. In general, in vitro leukocyte aggregation and in vivo neutropenia were considerably less sensitive assays. Chemotactic factor inactivator (CFI) purified from human serum destroyed in parallel all biological activities of C3 and C5 chemotactic factors but had no effect on the bacterial chemotactic factor and the activities of synthetic chemotactic peptides.