Stimulation of a cell-mediated cytotoxic response to FeLV-induced T cell lymphomas in the cat

Nonspecific cell-mediated cytotoxicity was examined in the peripheral blood and spleens of normal and vaccinia virus-infected adult domestic cats. Natural cytotoxic (NC)-like cells, as measured by lysis of vaccinia- or HSV-infected, adherent cat tongue cells, were found in both the spleen and peripheral blood of normal, nonimmune cats. Cytotoxicity was expressed in a 16-hr assay but not in a 4-hr assay. Natural killer (NK)-like cells, as measured by lysis of an FeLV-induced lymphoid tumor cell line (FL-74) growing in suspension, were found in the spleen but not PBL, and required a 16-hr assay for expression. Infection with vaccinia virus did not increase the activity of feline NC-like cells in either the peripheral blood or the spleen. NK-like function, however, was increased. Cytotoxicity peaked 6 days post-infection and required a 16-hr assay for maximal expression of cell lysis. Furthermore, a cell with cytotoxic characteristics of the spleen NK-like cell appeared at low levels in the circulation at 6 days post-vaccinia infection. NK-like cells from vaccinia-infected cats showed some cytotoxicity for FL74 targets in a 4-hr assay. The cat thus possesses at least two functionally different populations of naturally cytotoxic cells. NC-like cells are found in the spleen and peripheral blood, lyse virus-infected monolayer targets, and are not activated by infection. NK-like cells are found in the spleen, lyse-lymphoid tumor targets, and can be activated by infection, with their peak activity occurring 6 days after infection.     

Migration of putative progenitor T cells in response to thymus-derived chemotactic factors

Progenitor T cells reach the thymus through the circulation from hematopoietic organs and then migrate toward the site of differentiation in the thymus. The mechanism that regulates such intrathymic migration is not well understood. In order to clarify this mechanism, in vitro chemotactic activity for murine thymocytes was assayed in the extracts and culture supernatants of thymic tissue elements. A potent thymocyte chemotactic activity was found in the extract and culture supernatant from Ig-, Ia- thymic stromal cells. Peanut agglutinin-positive (PNA+1), Thy 1+, TL-, Lyt 1+2-, L3T4- thymocytes, Ig-, Thy 1- bone marrow cells, and mononuclear cells of spleen and peripheral blood, but neither B cells nor lymph node cells, were chemotactically attracted by the factor(s). The chemotactic activity was found in none of the following materials tested: the extract and culture supernatant of thymocytes, culture supernatant of lymph node stromal cells, normal mouse serum, and zymosan-activated serum. The chemotactic activity was found in three molecular fractions by gel chromatography. The activity in all three fractions was destroyed by trypsin digestion or by heating at 56 degrees C for 30 min. These results suggest that Ig-, Ia- thymic stromal cells but not thymocytes secrete a chemotactic factor(s) for progenitor T cells with three molecular species. The factor is considered to play an important role in the migration of intrathymic progenitor T cells into the site of differentiation.     

In vitro stimulation of natural killer (NK) cells by soluble factor(s) generated in antigen-stimulated rhesus monkey peripheral blood lymphocyte cultures.

Peripheral blood lymphocytes from rhesus monkeys (Macaca mulatta) sensitized to keyhole limpet hemocyanin (KLH), when stimulated in vitro with KLH, developed natural killer (NK) cell activity that was assayed with Rous Sarcoma virus-transformed marmoset fibroblasts as targets in a 4-hr 51Cr-release assay. The supernatant fluids from 24- to 25-hr KLH-activated cultures were capable of stimulating NK development in nonsensitive lymphocyte cultures. The effector cells were neither macrophages nor B cells (plastic and nylon-wool nonadherent) and did not form E-rosettes with neuraminidase-treated sheep red blood cells. Cultures depleted of EA-rosetting cells, i.e., Fc-receptor-bearing lymphocytes, were incapable of generating NK activity when stimulated in vitro. Kinetic studies showed that peak DNA synthesis, as measured by 3H-T incorporation, preceded maximum cytotoxicity. Elimination of dividing cells by 5-bromo-2'deoxyuridine (BrdU) and light treatment during the interval from day 1 to day 4 inhibited the development of cytotoxicity on day 7. Cell replication was required for the induction of NK cells with KLH as well as with antigen-activated culture supernatant fluids. When cultures were left unstimulated for 4 days, NK activity could not be developed subsequently either by adding antigen, mitogen (PHA), or supernatant fluids from activated cultures.     

Generation and differentiation of IL-17-producing CD4+ T cells in malignant pleural effusion

IL-17-producing CD4(+) T (Th17) cells have been found to be increased in some human cancers; however, the possible implication of Th17 cells in regulating antitumor responses in malignant pleural effusion (MPE) remains to be elucidated. In the current study, distribution and phenotypic features of Th17 cells in both MPE and peripheral blood from patients with lung cancer were determined by flow cytometry or double immunofluorescence staining. The impacts of cytokines on Th17 cell generation and differentiation were explored. The chemoattractant activity of chemokines CCL20 and CCL22 for Th17 cells in vitro was also observed. It was found that the increased Th17 cells could be found in MPE compared with blood. The in vitro experiments showed that IL-1β, IL-6, IL-23, or their various combinations could promote Th17 cell generation and differentiation from naive CD4(+) T cells. MPE was chemotactic for Th17 cells, and this activity was partly blocked by anti-CCL20 and/or CCL22 Abs. Our data also showed that the accumulation of Th17 cells in MPE predicted improved patient survival. It could be concluded that the overrepresentation of Th17 cells in MPE might be due to Th17 cell differentiation and expansion stimulated by pleural proinflammatory cytokines and to recruitment of Th17 cells from peripheral blood induced by pleural chemokines CCL20 and CCL22. Furthermore, the accumulation of Th17 cells in MPE predicted improved patient survival. These data provide the basis for developing immune-boosting strategies based on ridding the cancer patient of this cell population.     

Study of chemotactic activity developed by neutrophils from rheumatoid arthritis patients

Neutrophils are the predominant cells accumulated in the synovial fluid (SF) of rheumatoid arthritis (RA) patients. Accumulation of neutrophils may be regarded as a possible way by which neutrophils exert cytotoxic functions. The aim of the present study was to analyze the chemotactic response of neutrophils (PMNs) isolated from the peripheral blood or SF of patients with RA by performing the chemotaxis assay, in which N-formyl-methionyl-leucyl-phenylalanine (FMLP) was used as chemotactic agent. Our results showed that FMLP induced response of peripheral blood neutrophils from 12 patients with RA was similar with the response of 15 healthy controls. A decreased chemotactic response to FMLP was, however, observed in PMNs isolated from the SF of RA patients as comlipared with peripheral blood cells. Therefore, this defective chemotactic ability of neutrophil, was inversely correlated with the number of infiltrating cells in SF. These results indicate that chemotactic ability of neutrophils may be reduced after migration to the SF. Because PMNs chemotaxis in vivo has likely occurred in the presence of serum or SF, we tried to simulate the same conditions in vitro. Therefore, we analyzed the effect of serum or SF on the RA-PMNs chemotaxis. Heat-inactivated serum produced a marked reduction of chemotactic activity developed by PMNs isolated from patients with RA. Notably, a significant increase of chemotactic activity was observed when FMLP and serum stimuli were used together, as compared with the same stimuli used alone. The results suggested that complement activation might interfere with neutrophils chemotaxis. SF amplifies the chemotactic activity of PMNs isolated from peripheral blood of RA patients, but does not affect the chemotaxis developed by PMNs isolated from SF. The data might suggest that several components of SF (IL-8, leukotrien B4, thrombin, platelet-activating factor, etc.) could serve as a potent stimulus for recruitment of neutrophils from periphery into the RA joint. In conclusion, serum or SF components seem to contribute to chemotaxis of neutrophils and play a role in differential killing of PMNs and incidence of infection.     

A chemotactic factor for rat thymocytes may regulate T-lymphocyte migration toward the thymic microenvironment

Using a modified Boyden chamber assay, extracts or culture supernatants of rat thymic stromal cells, or thymocytes were examined by chemotactic activity to rat leukocytes. Rat thymocytes responded chemotactically to the aqueous extract as well as to culture supernatants of thymic stromal cells. However, neither the extract and culture medium from concanavalin A-stimulated thymocytes nor any component of rat serum has shown such an activity. The thymic extract was fractionated into three molecular species with chemotactic activity for thymocytes. The thymocyte chemotactic factor(s) (TCFs) in the extract was distinct from known lymphocytic chemotactic factors, such as interleukin-1 (IL-1), IL-2, C5a, and the culture supernatant of stimulated thymocytes. In vitro, TCFs could attract, in addition to thymocytes, bone marrow cells, fetal liver cells, and nylon-wool nonadherent lymphocytes from peripheral blood and spleen. Lymph node cells, neutrophils, macrophages, and B cells from peripheral blood could not respond to TCFs. Thymocytes also responded to the extract of splenic stromal cells. Unlike the thymic extract, however, the splenic extract was chemotactically active for lymphocytes from lymph nodes but not for bone marrow cells. These results indicate that thymic stromal cells secrete a chemotactic factor(s) for a relatively immature type of T-lineage cells, which may by a thymus-homing progenitor T cell, while spleen may contain an attractant for a relatively mature type of T-lineage cells.     

In vitro activation of suppressor cells from spleens of mice treated with radioactive strontium

Mice were treated with two 100-muCi injections of 89Sr to deplete marrow-dependent (M) cells. Mice so treated responded normally to immunization with sheep red blood cells (SRBC) in vivo; moreover, spleen cells from 89Sr-treated mice were able to respond to SRBC after infusion into irradiated recipient mice. However, spleen cells from mice treated with 89Sr did not respond to SRBC in vitro and mixtures of normal spleen cells with the latter were also not able to respond in vitro. The discrepancy between in vivo and in vitro responses was abolished by culturing spleen cells for 24 hr before testing their ability to respond to SRBC in the adoptive transfer in vivo. Pretreatment of spleen cells from 89Sr-treated mice with 1000 R of gamma-radiation lessened their suppressive activity. The suppressor cells were detected in spleens of athymic nude mice treated with 89Sr. The suppressive activity, after the 24-hr culture period, was not abolished by irradiation and was active in vivo as well as in vitro. Thus, depletion of M cells by 89Sr results in the appearance within the spleen of thymus-independent suppressor cells, which require a short period of in vitro cultivation before becoming functionally active.     

Modulation of monocyte chemotactic function in inflammatory lesions. Role of inflammatory mediators

Monocyte recruitment and accumulation in the synovial tissue is pivotal in the evolution of rheumatoid arthritis (RA). In the present study we examined the chemotactic potential of monocytes obtained from synovial fluid (SF) of patients with RA. Functionally, SF monocytes exhibited greatly diminished chemotactic activity to C5a compared with monocytes from the peripheral blood. In contrast, their chemotactic responsiveness to the synthetic peptide, FMLP, was nearly normal. To define a mechanism for this differential chemotactic dysfunction, cell-surface receptors for C5a (C5aR) and FMLP (FMLP-R) were evaluated. Whereas FMLP-R expression was similar on both blood and inflammatory monocytes, C5aR expression was markedly reduced on SF cells. Because decreased C5a binding in certain RA SF samples could not be attributed to free C5a, known or suspected components of inflammatory SF were evaluated for their ability to modulate chemotactic ligand receptors. Bacterial products including LPS and streptococcal cell walls, which are potent monocyte activators, down-regulated C5aR without affecting FMLP-R. Moreover, the cytokines IFN-gamma and granulocyte-macrophage-CSF selectively decreased C5aR in parallel with decreased in vitro chemotactic activity to C5a. Thus, these data indicate that 1) synovial effusions may contain C5a and/or inflammatory mediators that modulate phenotypic and functional changes in monocytes, 2) chemotactic ligand receptors are independently regulated in inflammatory lesions, and 3) decreased C5aR expression and chemotactic potential likely provide a mechanism whereby monocyte-macrophages persist within the inflamed synovium.     

The decreasedin vitro chemotactic activity of polymorphonuclear leukocytes of newborns and infants

Using Boyden's technique, a statistically significant decrease in the chemotactic activity of polymorphonuclear (PMN) leukocytes was found during the early postnatal period, i.e. in the cord blood and in blood of newborns within the first 10-15 d of life after stimulation of cells with both zymosan-activated adult serum (ZAS) and with an abacterial filtrate of Escherichia coli broth culture (ECF). After this period, the responsiveness of leukocytes to both chemotactic agents increased and remained at the same level during the whole observation period, i.e. up to the age of 6 months. Nevertheless even then it did not reach fully the responsiveness of the leukocytes of mothers and pregnant women. Zymosan-activated serum was shown to be a more potent chemotactic stimulus to leukocytes of infants as compared to the E. coli filtrate.     

Functional analysis of mononuclear cells infiltrating into tumors. V. A. soluble factor involved in the regulation of cytotoxic/suppressor T cell infiltration into tumors

We have analyzed the mechanisms controlling the accumulation of cytotoxic/suppressor T lymphocytes in tumor tissues. We found that tumor-infiltrating helper/inducer T cells isolated from T-9 gliosarcoma-sensitized rats between 4 and 6 days after T-9 gliosarcoma inoculation produced a lymphocyte migration factor (LMF) during in vitro culture. Four peaks of LMF activity (A through D) were detected upon fractionation of LMF by using a Mono Q anion exchange column chromatography. Peak C exhibited the strongest activity among the four peaks of LMF. The action of peak C was chemotactic, but not chemokinetic. Peak C had an isoelectric point of 8.0 and a Mr of 26,000 Da. Only cytotoxic/suppressor T cells were found to be sensitive to peak C in vitro as well as in vivo. It is thus likely that peak C is responsible for the infiltration of cytotoxic/suppressor T cells into tumor tissues. The infiltration of lymphocytes into tumor tissues might also be regulated by the expression of lymphocyte sensitivity for LMF. The target molecule for LMF at 4 days may involve an asparagine-linked oligosaccharide.     

Cellular changes in bone marrow of malaria-infected mice. III. Chemotaxis of granulocytes

The number of bone marrow cells and their chemotactic activity was studied during malaria infection. Two days after infection of Balb/c mice with Plasmodium berghei, an increase in granulocyte number was observed in the blood. A modified Boyden chamber chemotaxis assay was employed to investigate the mechanism of granulocyte accumulation in the blood. Bone marrow cells from normal mice, from mice during a primary lethal infection and from immune mice after challenge were compared. The complement factor C5a showed chemotactic activity for bone marrow cells; a significant decrease of chemotaxis was only observed after 6 days of primary infection. Extracts of spleen, liver and infected erythrocytes lacked chemotactic activity, or caused inhibition of cell migration. Serum from mice with a 2-day primary infection contained chemotactic activity. The active component was heat labile, protease sensitive and had an estimated molecular weight of 250,000.     

Macrophage chemotactic factor (MCF) produced by a human T cell hybridoma clone

A human T cell hybridoma clone, D6-18, producing high levels of macrophage chemotactic factor (MCF) was established by the emetine-actinomycin D selection method. MCF was found to be present not only in the culture medium but also in the cell lysate of D6-18 cells. The secretion of the MCF from D6-18 cells was effectively inhibited by disodium cromoglycate, which is an inhibitor of the degranulation of mast cells, suggesting that MCF is stored in granules. The MCF of D6-18 cells was purified from the sonicated cell lysate by ion-exchange chromatographies and high-performance liquid chromatography. The amino acid sequence of the purified MCF was revealed to be WLGREDGSE or WLGRQDGSE. The synthetic peptide WLGREDGSE showed chemotactic activity against guinea pig macrophages and human monocytes at the concentration of about 10(-8) M.     

Evidence for a non-steroidal angiotropic factor from the primate corpus luteum: stimulation of endothelial cell migration in vitro

After luteal cells from 7 midluteal phase cynomolgus monkeys were cultured for 72 h, luteal conditioned media were found to contain angiotropic activity that stimulated endothelial cell migration in vitro, using a 48-microwell chemotaxis assembly. The number of endothelial cells that migrated through 8 micron-pore polycarbonate membranes in 2 h was three-fold greater (P less than 0.01) with luteal cell-conditioned vs identical unconditioned media. Pre-treatment of luteal cultures with hCG, FSH, or testosterone did not enhance production of the endothelial cell migration stimulating activity (P greater than 0.25). Luteal angiotropic activity was both chemotactic and chemokinetic. Angiotropic activity was retained in steroid-depleted fractions after reversed-phase chromatography. These results demonstrate that monkey luteal cells secrete a non-steroidal factor(s) which directly stimulate(s) migration of endothelial cells in vitro. A luteal angiotropic factor may be an important intraovarian regulator of the formation and lifespan of the primate corpus luteum during the ovarian cycle.     

Production and characterization of recombinant human neutrophil chemotactic factor

A putative mature human neutrophil chemotactic factor (NCF) corresponding to the C-terminal 72 amino acids of its precursor was directly produced in Escherichia coli by recombinant DNA technology. Human NCF was present in both the soluble and insoluble protein fractions of the homogenate of host cells, and it was partially purified as a water-soluble polypeptide from both fractions, separately. The partially purified NCF preparation was highly purified to an endotoxin-free homogeneous polypeptide by means of CM-Sepharose CL-6B column chromatography and gel filtration on Toyopearl HW-55. No difference between the human NCF preparations purified from both starting materials could be found concerning purity, primary structure, solubility, molecular weight, and chemotactic activity for human neutrophils. The amino acid sequence of recombinant human NCF was identical to the sequence deduced from the cDNA sequence. A methionine residue due to the translation initiation codon was removed. Recombinant human NCF was found to be biologically active and to exhibit chemotactic activity for human neutrophils in vitro and cause a neutrophil infiltration in vivo in mice.     

Analysis of Chemotaxis in White Blood Cells

We wish to report the development of an assay system for the study of white blood cells in vitro. With this system we have demonstrated that a yet unidentified substance found in red blood cell membranes and cyclic adenosine monophosphate (cAMP) cause the chemotactic response in white blood cells. We have not yet determined whether the substance released from the membrane is cAMP.     

Mode of in vitro augmentation of natural killer cell activity by recombinant human interleukin 2: a comparative study of Leu-11+ and Leu-11- cell populations in cord blood and adult peripheral blood

Human newborn natural killer (NK) cell activity against K562 target cells was observed to be low compared with adult controls. Although Leu-7 (HNK-1)+ cells were negligible in cord blood, the proportions of Leu-11+ cells were equal to those of adult peripheral blood. Leu-11+ cells sorted from cord blood lymphocytes, as well as from adult lymphocytes exhibited the morphology of granular lymphocytes. In this study, we have investigated the phenotypic characterization of recombinant interleukin 2 (rIL 2)-induced cytotoxic lymphocytes against K562 cells by using anti-Leu-11 monoclonal antibody. Spontaneous cytotoxicity of lymphocytes was restricted to Leu-11+ cells in cord blood, as well as in adult blood, but this activity was low in cord blood Leu-11+ cells as compared with that of adult ones. NK cell activity of adult Leu-11+ cells could not be additionally enhanced after an 18-hr incubation with rIL 2(25 U/ml), whereas rIL 2 could potentiate the cytotoxicity of cord blood Leu-11+ cells approximately to the adult levels. It should be noted that cytotoxic activity of both Leu-11- cells from cord blood and adult blood that had no basal NK cells activity could be significantly potentiated by rIL 2. On the other hand, lymphokine-activated killer cells cytotoxic for HL-60 cell line could not be generated, and no proliferation of the lymphocytes was detected after an 18-hr incubation with rIL 2. It was shown that rIL 2 could not enhance the ability to bind to target cells in Leu-11+ and Leu-11- cells by means of a single cell conjugate assay, but the rate of target lysis of Leu-11+ cells from cord blood was significantly enhanced by rIL 2. These results suggested that rIL 2-induced cytotoxic effector cells were heterogeneous, and rIL 2 might potentiate the cytotoxicity of functionally immature NK cells or NK precursor cells.     

Human T-lymphocyte chemotactic activity: nature and production in response to antigen

Previous studies have shown that supernatants from concanavalin A-stimulated human peripheral blood mononuclear cells and isolated Leu-2 suppressor/cytotoxic T cells are chemotactic for Leu-3 helper/inducer T cells. The current study shows that lymphocyte chemotactic factor (LCF) is also produced following antigen (tetanus toxoid) challenge of mononuclear cells obtained from recently immunized human donors. LCF was detected in 24-hr supernatants from mononuclear cells challenged with tetanus and was produced maximally at 48 hr. Tetanus toxoid challenge of mononuclear cells obtained from individuals whom had not received a tetanus immunization for 7 to 10 years prior to testing showed little or no production of LCF. Serial studies of these individuals following a tetanus booster immunization showed that LCF was produced by antigen-challenged mononuclear cells obtained 1-5 days postimmunization, was produced optimally 5-15 days postimmunization, and was still produced by antigen-challenged mononuclear cells obtained 6 weeks later. Fractionation of mononuclear cells from immunized donors into glass wool nonadherent lymphocytes, T lymphocytes, and non-T lymphocytes showed that tetanus-toxoid-induced LCF was produced by nonadherent lymphocytes and T cells but not non-T cells. Further fractionation of T lymphocytes into Leu-2 and Leu-3 T-cell subpopulations showed that LCF production by antigen-challenged isolated subpopulations was limited to the Leu-2 suppressor/cytotoxic T-cell subset. Characterization of both Con A and tetanus toxoid-induced LCF by gel filtration on Sephadex G-100 demonstrated the presence of two peaks of LCF corresponding to molecular weights of approximately 14,000-17,000 and 40,000-50,000.     

Suppression of T lymphocyte chemotactic factor production by the opioid peptides beta-endorphin and met-enkephalin

The opioid peptides beta-endorphin and met-enkephalin have been shown to modulate human lymphocyte proliferation, mononuclear cell locomotion, natural killer cell activity, and neutrophil locomotion. This study demonstrates that beta-endorphin and met-enkephalin inhibit the production of a T lymphocyte chemotactic factor (LCF) by concanavalin A (Con A)-stimulated peripheral blood mononuclear cells. Inhibition of LCF production was observed by using concentrations of 10(-11) to 10(-6) M beta-endorphin or met-enkephalin but not alpha-endorphin. A bimodal pattern of suppression of LCF production was observed with both met-enkephalin and beta-endorphin when titrated from 10(-12) to 10(-6) M concentrations, with the peaks of suppressive activity occurring at concentrations of 10(-11) M and 10(-6) M. Timed studies of the production of LCF over a 54-hr period showed that there was an appreciable lag in the onset of measurable LCF activity in mononuclear supernatants produced in the presence of beta-endorphin and met-enkephalin. The suppression of LCF production mediated by opioid peptides in mononuclear supernatants was abrogated by depletion of glass-adherent mononuclear cells before culturing with opioids and Con A. The inhibitory effect of opioid peptides on LCF production was prevented by the addition of indomethacin to cell cultures. Additional experiments showed that exogenous prostaglandin E2 (PGE2) suppressed Con A-stimulated LCF production when added at concentrations ranging from 10(-6) to 10(-8) M. Other studies suggested that the mechanism of opioid peptide-mediated suppression of LCF production was due to an enhanced sensitivity of mononuclear cells to the inhibitory action of PGE2. These data provide further evidence for modulation of the immune response in humans by the neuroendocrine hormones beta-endorphin and met-enkephalin and further suggest a link between this modulation and arachidonic acid metabolism.     

Generation of lipid neutrophil chemoattractant by irradiated bovine aortic endothelial cells

Radiation injury to blood vessels is associated with an acute inflammatory process. We investigated the capacity of cultured bovine aortic endothelial cells (BAEC) to produce chemotactic factors after radiation injury. BAEC in serum-free media were irradiated with a cobalt-60 Gammacell 220 and the cell supernatants were assayed for chemotactic activity for human neutrophils in a Boyden chamber. There was a rapid release of chemotactic activity into the BAEC supernatants which was dependent both on the dose of radiation (5 to 40 Gy) and the time between irradiation and sample collection. In contrast, isolation of BAEC lysates by freeze-thawing was not associated with the presence of similar chemotactic activity. The chemotactic activity released from the irradiated BAEC was not destroyed by boiling nor by treatment with trypsin. The release of the chemotactic activity was, however, inhibited by the addition of a lipoxygenase inhibitor but not by the addition of a cyclooxygenase inhibitor before the irradiation. The chemotactic activity was recovered from the cell supernatants in the lipid phase after extraction with chloroform/methanol. Furthermore, the chloroform/methanol extracts co-eluted with authentic leukotriene B4 when the BAEC were prelabeled with [14C] arachidonic acid. However, we were unable to detect endogenous leukotriene B4 with RIA. Instead, the only detectable endogenous lipid present in the supernatants was 13-hydroxyoctadecadienoic acid which is derived from linoleic acid via the lipoxygenase pathway. 13-Hydroxyoctadecadienoic acid, however, had no chemotactic activity. These findings suggest that endothelial cells rapidly release a chemotactic agent after irradiation, the release of which is associated with a lipoxygenase pathway. The release of this chemotactic activity may account in part for the acute inflammatory response that is observed after ionizing irradiation.