Purification of human blood basophils by single step isopycnic banding on Percoll

Human venous blood, anticoagulated with EDTA, was layered onto a discontinuous Percoll gradient, made from solutions of density 1.088, 1.079, and 1.070 gm/ml. After centrifugation at 700g for 15 min at 22 degrees C, the majority of the blood basophils was found in a narrow band at the density 1.070-1.079 interface (Percoll band 2). For 15 normal donors, mean total basophil number recovered from all locations in the gradient was 3.8 +/- 1.2 (SD) X 10(4) basophils per ml of blood applied. Thus, 95% of the values ranged from 1.5 to 6 X 10(4), which compares favorably with the reported range of 1 to 8 X 10(4) basophils per ml for normal subjects. In the basophil-rich Percoll band 2, 2.8 +/- 0.8 X 10(4) basophils were recovered per ml of blood applied. The mean percentage of basophils in Percoll band 2 was 19%, with a range of 5 to 53%. Monocytes and neutrophils were present in very small numbers; the majority of accompanying cells were small lymphocytes.

N-formylmethionyl-leucyl-[3H]phenylalanine binding, superoxide release, and chemotactic responses of human blood monocytes that repopulate the circulation during leukapheresis

Human blood monocytes comprise two subpopulations: one migrates to the chemoattractant, N-formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe), and has saturable binding sites for this peptide; the other does not migrate and exhibits little peptide binding. To determine if expression of binding sites was a function of monocyte maturation, we depleted human subjects of blood monocytes by leukapheresis so that the circulation was repopulated by monocytes released from the bone marrow. Pre- and postleukapheresis monocytes were then compared for fMet-Leu-[3H]Phe binding, superoxide generation, and chemotactic responses. No significant differences in peptide binding curves were found, suggesting that receptor expression was stable over the maturational span represented by these two groups of cells. This supports the hypothesis that there are two distinct lineages of monocytes with respect to expression of receptors for fMet-Leu-Phe. An additional finding of interest was that the number of chemotactically responsive cells immediately postleukapheresis was half the control. This was a transient state; monocyte responses were normal 3 hr after termination of leukapheresis, suggesting that they rapidly become functionally mature.

A high molecular weight chemoattractant generated from C5 by ultracentrifugation of mouse serum without activation of complement

After ultracentrifugation of normal mouse serum, we found chemoattractant activity in the high molecular weight protein region at the bottom of the tube, which was comparable in amount and potency to the attractant in endotoxin-activated serum. This was not a pre-formed attractant, but was generated from serum reactants at least one of which was inactivated by heating at 56 degrees C. Analysis of sera from 10 different mouse strains for hemolytic C5 activity and for capacity to generate chemoattractant on ultracentrifugation showed that the 4 strains without C5 were the only strains that failed to generate the attractant. Thus, the attractant precursor is C5. Since the activity was generated in the presence of 0.01 M EDTA, classical or alternative complement activation was not required. The chemoattractant product had a mol. wt of approximately 170,000; it was therefore not free C5a. These results, and data recently published on digestion of purified human C5 by trypsin, suggest that limited proteolysis of C5 can produce a chemoattractant molecule without release of free C5a.

Molecular weight, isoelectric point, and stability of a murine lymphokine that induces macrophage tumoricidal activity

A factor in antigen- or mitogen-stimulated murine spleen cell culture supernatants that induces macrophage-mediated tumor cytotoxicity was characterized physicochemically. Although activity was eluted from Sephadex G-100 columns in a region corresponding to a MW of 55,000, rechromatography of the first and second halves of the eluted peak resulted in two separate peaks, corresponding in location to the first and second halves of the original peak. This shows that the original peak comprises two activation factors of slightly different MW. In contrast, electrofocusing experiments designed to assure that the isoelectric position had been reached by the end of the run showed a single isoelectric point of pH 5.8, with no sign of charge heterogeneity. Denaturation studies showed rapid loss of activity at 60 degrees C, stability over a pH range of 5 to 10, loss of activity at pH 4.0, and loss of two-thirds of the activity in 6 M urea. The number of criteria by which this lymphokine has now been characterized should suffice to distinguish it from other lymphokines evaluated by similar methods.

Colony-stimulating factors and regulation of macrophage tumoricidal and microbicidal activities

Conditioned medium from antigen- or mitogen-stimulated spleen cells, lymphokines, contained factors that induced formation of granulocyte and macrophage colonies in cultures of bone marrow cells (CSF). Lymphokines also contained factors that induced macrophage non-specific tumoricidal activity against fibrosarcoma 1023, antibody-dependent tumoricidal activity against lymphoma 18-8, and antimicrobial activities against amastigotes of the protozoan parasite, Leishmania tropica. The factors that regulated macrophage effector functions, however, were different from those that induced colony formation, and could be distinguished from CSF by Sephadex gel chromatography or heat sensitivity. To further analyze a role for CSF in induction of macrophage effector activities, conditioned medium from several nonlymphoid cell sources (L-929, WEHI-3, and endotoxin-treated lung cells) were assayed for CSF activities and capacity to induce tumoricidal and microbicidal activities. Conditioned medium that contained either macrophages CSF (CSF-1) or the factor that induced formation of both macrophage and granulocyte colonies failed to activate macrophages for effector activities against fibrosarcoma 1023, lymphoma 18-8, and L. tropica amastigotes (either resistance to infection or intracellular destruction). These data suggest that CSF has no direct role in activation of macrophages for tumoricidal and microbicidal activities against these targets.

Production of mouse lymphotoxin by phytohemagglutinin-stimulated spleen cells requires two cell fractions

The appearance of lymphotoxin in the culture fluid of phytohemagglutinin (PHA)-stimulated mouse spleen cells required two cell fractions that were separated by adherence to plastic. Upon stimulation with PHA, neither cell fraction alone produced significant amounts of lymphotoxin; however, when the cell fractions were combined and then stimulated with PHA, full activity was produced. Cytotoxic activity was not fully restored by combining PHA-stimulated cultured fluids from adherent and nonadherent cell fractions. This indicated that the cytotoxic activity was not the result of two factors, one produced by each cell fraction, that acted on the target cells, but rather, two cells interacted to produce lymphotoxin. Treatment of the unfractionated spleen cells with monoclonal anti-Thy1.2 and complement before PHA stimulation greatly reduced the production of lymphotoxin and indicated that at least one of the cells was a T cell. Lymphotoxin production was partially restored by the addition of nonadherent cells to the anti-Thy1.2-treated cells, suggesting that the T cell was nonadherent. Treatment of unfractionated cells with either silica or carrageenan had no effect on the subsequent production of lymphotoxin by PHA, suggesting that the adherent cell was not actively phagocytic.

Two neutrophil populations in human blood with different chemotactic activities: separation and chemoattractant binding

Normal human blood contains a population of neutrophils that migrates to various chemoattractants and a population that fails to migrate. The percentage of neutrophils migrating to optimal concentrations of chemoattractants was quantified: 20 to 40% migrated to N-formylmethionyl-leucyl-phenylalanine, 30 to 50% migrated to human C5a, 25 to 35% migrated to human leukocyte-derived chemotactic factors, 20 to 30% migrated to casein, 15 to 20% migrated to pepstatin, and 1 to 5% migrated to medium alone. Neutrophil migration to the most active chemoattractant was not increased when other chemoattractants were added, indicating that the population of neutrophils migrating to the most active attractant was the same population that was migrating to the other attractants. The percentage of neutrophils migrating to a chemoattractant was not altered by prolonging the assay incubation period or by replacing the attractant with new chemoattractant during the assay, and the percentage was independent of the neutrophil concentration added to the chemotaxis chamber. Nonmigrating neutrophils were isolated with a chemotaxis collection chamber, and they were examined for radiolabeled chemotactic peptide binding. The binding of radiolabeled N-formylmethionyl-leucyl-phenylalanine by nonmigrating and migrating neutrophils was identical.

Only the chemotactic subpopulation of human blood monocytes expresses receptors for the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine

Human peripheral blood monocytes comprise a subpopulation of 20 to 40% that is capable of responding to chemoattractants and a remaining subpopulation that cannot respond. We were able to obtain 99%-pure attractant-responsive monocytes by using a newly constructed separation chamber. The binding of the radioactive chemotactic peptide N-formylmethionyl-leucyl-[3H]phenylalanine to migrating and nonmigrating populations was then studied. The binding was saturable at room temperature in the presence of azide. Saturation occurred at 5 x 10(-8) M, and 50% of the maximal binding was obtained at 10(-8) M, the concentration that induced optimal chemotaxis. The nonmigrating monocytes did not bind the peptide under the same conditions, which shows that at least one reason for a nonresponsiveness to chemotaxin is apparently a lack of receptors. By Scatchard analysis we calculated an equilibrium dissociation constant ranging from 23 to 37 nM; the number of binding sites per cell ranged from 64,000 to 77,000. The binding was very rapid. Fifty percent of the optimal binding occurred at 3.5 min, and equilibrium was reached after 20 to 30 min. Chemotactic deactivation of the monocytes reduced the number of available binding sites by 60%.

Chemotaxis of purified human monocytes in vitro: lack of accessory cell requirement

This study was undertaken to determine whether cell cooperation, either among monocytes or between monocytes and lymphocytes, is a prerequisite for monocyte chemotactic responsiveness. We compared Ficoll-Hypaque-separated mononuclear cells and a preparation of 99% pure monocytes obtained by chemotaxis in a newly designed separation chamber. Monocytes of both preparations migrated to chemoattractants without a lag phase, and no further increase in migrated cells was observed after 70 min. The cell dose-response was linear for both preparations over a wide range of cell concentrations in the cell input well of the chemotaxis chamber, suggesting that no monocyte-monocyte interaction was required. Since only 20 to 60% of the monocytes purified by chemotaxis migrated a second time, the possibility of a requirement for an accessory cell was tested. The addition to purified monocytes of several different mononuclear cell preparations comprising lymphocytes or nonmigrating monocytes had no effect on monocyte migration. These experiments show that normal human blood monocytes in vitro do not require stimuli from other cells to respond to chemoattractants. Their behavior is profoundly different from that of mouse peritoneal macrophages, which exhibit a time lag in vitro before migration toward an attractant and become more responsive with either increasing cell concentration or addition of purified lymphocytes.

Intracellular replication and lymphokine-induced destruction of Leishmania tropica in C3H/HeN mouse macrophages

C3H/HeN resident peritoneal macrophages in suspension culture supported continuous replication of L. tropica amastigotes; the total number of intracellular parasites increased 8- to 10-fold over 96 hr in culture. Lymphokine treatment of macrophages markedly affected intracellular replication of the Leishmania. Cultures treated with lymphokines before exposure to L. tropica were more resistant to infection, and 35% fewer cells contained intracellular amastigotes compared to medium-treated controls. Lymphokine-pretreated cells that became infected also inhibited the replication of intracellular amastigotes. Macrophage cultures treated with lymphokines after infection exhibited potent microbicidal activity; 75 to 80% of macrophages were free of intracellular parasites by 72 hr. Fractionation of lymphokine supernatants by Sephadex G-100 demonstrated 3 areas of activity for the induction of macrophage intracellular killing (130,000, 45,000, less than or equal to 10,000 daltons); one of these activity peaks (45,000-m.w. lymphokine(s)) also induced increased resistance to infection with L. tropica.

Intracellular replication and lymphokine-induced destruction of Leishmania tropica in C3H/HeN mouse macrophages

C3H/HeN resident peritoneal macrophages in suspension culture supported continuous replication of L. tropica amastigotes; the total number of intracellular parasites increased 8- to 10-fold over 96 hr in culture. Lymphokine treatment of macrophages markedly affected intracellular replication of the Leishmania. Cultures treated with lymphokines before exposure to L. tropica were more resistant to infection, and 35% fewer cells contained intracellular amastigotes compared to medium-treated controls. Lymphokine-pretreated cells that became infected also inhibited the replication of intracellular amastigotes. Macrophage cultures treated with lymphokines after infection exhibited potent microbicidal activity; 75 to 80% of macrophages were free of intracellular parasites by 72 hr. Fractionation of lymphokine supernatants by Sephadex G-100 demonstrated 3 areas of activity for the induction of macrophage intracellular killing (130,000, 45,000, less than or equal to 10,000 daltons); one of these activity peaks (45,000-m.w. lymphokine(s)) also induced increased resistance to infection with L. tropica.

Chemotaxis by mouse macrophage cell lines

Five mouse macrophage cell lines were tested for chemotaxis and phagocytosis. All 5 cell lines ingested sheep red cells coated with rabbit IgG anti-Forssman antibody and exhibited chemotaxis to endotoxin-activated mouse serum (EAMS) and lymphocyte-derived chemotactic factor. Two cell lines were tested for chemotaxis to f-Met-Leu-Phe and neither responded. Four of the cell lines (RAW264, RAW309CR, PU5-1R, and WR19M.1) exhibited chemotaxis to C5a. These cell lines displayed a 1- to 2-hr lag before migrating toward EAMS, and chemotaxis was dependent upon cell density. When fewer than 10(3) cells were present per mm2 of filter surface, less than 10% of the cells migrated; however, at a density of 5 X 10(3) cells/mm2 50 to 70% of the cells migrated. WEHI-3 differed from the other cell lines in that there was no chemotaxis to C5a, migration to EAMS did not have a detectable lag, and there was no cell density dependence for chemotaxis. Comparison of these chemotactic properties with those reported in the literature for mouse macrophages and monocytes suggests that RAW264, RAW309CR, PU5-1R, and WR19M.1 have properties that are similar to those of mouse resident macrophages, whereas WEHI-3 may have some of the properties of mouse monocytes.

Chemotaxis by mouse macrophage cell lines

Five mouse macrophage cell lines were tested for chemotaxis and phagocytosis. All 5 cell lines ingested sheep red cells coated with rabbit IgG anti-Forssman antibody and exhibited chemotaxis to endotoxin-activated mouse serum (EAMS) and lymphocyte-derived chemotactic factor. Two cell lines were tested for chemotaxis to f-Met-Leu-Phe and neither responded. Four of the cell lines (RAW264, RAW309CR, PU5-1R, and WR19M.1) exhibited chemotaxis to C5a. These cell lines displayed a 1- to 2-hr lag before migrating toward EAMS, and chemotaxis was dependent upon cell density. When fewer than 10(3) cells were present per mm2 of filter surface, less than 10% of the cells migrated; however, at a density of 5 X 10(3) cells/mm2 50 to 70% of the cells migrated. WEHI-3 differed from the other cell lines in that there was no chemotaxis to C5a, migration to EAMS did not have a detectable lag, and there was no cell density dependence for chemotaxis. Comparison of these chemotactic properties with those reported in the literature for mouse macrophages and monocytes suggests that RAW264, RAW309CR, PU5-1R, and WR19M.1 have properties that are similar to those of mouse resident macrophages, whereas WEHI-3 may have some of the properties of mouse monocytes.

Specificity and reversibility of chemotactic deactivation of human monocytes

The chemotactic deactivation of human monocytes was studied to provide insight into the mechanism of chemotaxis. Deactivation was dependent on the dose of chemoattractant and time of incubation. A concentration in the cell suspension of 10(-8) M N-formylmethionylleucyl phenylalanine (FMLP) for 45 min at 37 degrees C led to 60% suppression of the subsequent specific chemotactic response. Higher concentrations of FMLP led to almost 100% specific suppression. Deactivation was specific under all conditions used. The response to a nonrelated chemoattractant, human serum-derived C5a, was unaffected by incubation in FMLP. Deactivation was also transient. If cells were deactivated at 37 degrees C with FMLP, they recovered within 6 h at 37 degrees C from this deactivation. Both phenomena, deactivation and recovery from deactivation, were temperature dependent. Monocytes could not be deactivated at 0 degrees C, and they did not recover from deactivation when kept at 0 degrees C. Thus, specific deactivation appears to require cellular metabolism, involving loss of receptors or blocking of a step between receptor occupancy and response.

Macrophages in resistance to rickettsial infections: characterization of lymphokines that induce rickettsiacidal activity in macrophages

Lymphokine-rich culture supernatants of antigen- or mitogen-stimulated spleen cells were fractionated by Sephadex G-200 column chromatography; fractions were assayed for capacity to induce tumoricidal and rickettsiacidal activities in mouse macrophages. Lymphokine activity that activated macrophages for tumor cytotoxicity eluted as a single peak in the 45,000 m.w. region. In contrast, activity for intracellular killing of rickettsiae eluted in 3 distinct regions: 115 to 125,000, 35 to 45,000, and less than 10,000 daltons. This elution pattern was observed with both antigen and mitogen-induced lymphokines. Activity of each of the 3 lymphokine species for induction of rickettsiacidal activity was destroyed by heating at 56 degrees C for 1 hr. Tumor cytotoxicity and rickettsiacidal activity, both effector functions of activated macrophages, were dissociated on the basis of lymphokines regulating these activities.

Macrophages in resistance to rickettsial infections: characterization of lymphokines that induce rickettsiacidal activity in macrophages

Lymphokine-rich culture supernatants of antigen- or mitogen-stimulated spleen cells were fractionated by Sephadex G-200 column chromatography; fractions were assayed for capacity to induce tumoricidal and rickettsiacidal activities in mouse macrophages. Lymphokine activity that activated macrophages for tumor cytotoxicity eluted as a single peak in the 45,000 m.w. region. In contrast, activity for intracellular killing of rickettsiae eluted in 3 distinct regions: 115 to 125,000, 35 to 45,000, and less than 10,000 daltons. This elution pattern was observed with both antigen and mitogen-induced lymphokines. Activity of each of the 3 lymphokine species for induction of rickettsiacidal activity was destroyed by heating at 56 degrees C for 1 hr. Tumor cytotoxicity and rickettsiacidal activity, both effector functions of activated macrophages, were dissociated on the basis of lymphokines regulating these activities.

Human monocyte chemotaxis: migrating cells are a subpopulation with multiple chemotaxin specificities on each cell

Only 20 to 40% of human blood monocytes were capable of responding to chemotaxins in vitro. This limit is not due to restrictions of the in vitro system, but is due to the existence of a migrating subpopulation. Over a wide range, the number of cells migrating toward a given concentration of chemotaxin was directly proportional to the number added to the chemotaxis chamber. These monocytes responded to all of the three stimuli used: human serum-derived C5a, human lymphocyte-derived chemotactic factor, and a synthetic peptide. It was possible to deactivate cells to one attractant, leaving the response to other attractants intact. This suggested that these attractants were recognized by different receptors. Several lines of evidence showed that most migrating cells had receptors for all three chemotaxins tested. Thus, if cells were assayed for migration to one attractant, no additional migration occurred when the remaining cells were assayed for migration to a different attractant. Furthermore, the same cells that had migrated toward one attractant were able to respond to other chemotaxins. We also found that a single attractant attracted as many cells as a combination of two or three attractants. Calculations from these data showed that at least 75% of the migrating monocytes have different receptors for all three attractants.