Current views on the ontogeny of macrophages and the humoral regulation of monocytopoiesis

Identification of organs of origin of macrophages that produce presepsin via neutrophil extracellular trap phagocytosis

Presepsin (P-SEP) is a specific biomarker for sepsis. Monocytes produce P-SEP by phagocytosing neutrophil extracellular traps (NETs). Herein, we investigated whether M1 macrophages (M1 MΦs) are the primary producers of P-SEP after NET phagocytosis. We co-cultured M1 MΦs and NETs from healthy participants, measured P-SEP levels in the culture medium supernatant, and detected P-SEP using western blotting. When NETs were co-cultured with M1 MΦs, the P-SEP level of the culture supernatant was high. Notably, we demonstrated, for the first time, the intracellular kinetics of P-SEP production by M1 MΦs via NET phagocytosis: M1 MΦs produced P-SEP intracellularly 15 min after NET phagocytosis and then released it extracellularly. In a sepsis mouse model, the blood NET ratio and P-SEP levels, detected using ELISA, were significantly increased (p < 0.0001). Intracellular P-SEP analysis via flow cytometry demonstrated that lung, liver, and kidney MΦs produced large amounts of P-SEP. Therefore, we identified these organs as the origin of M1 MΦs that produce P-SEP during sepsis. Our data indicate that the P-SEP level reflects the trend of NETs, suggesting that monitoring P-SEP can be used to both assess NET-induced organ damage in the lungs, liver, and kidneys during sepsis and determine treatment efficacy.

Effect of age on the frequency, cell cycle, and lineage maturation of rhesus monkey (Macaca mulatta) CD34+ and hematopoietic progenitor cells

The effects of maturation and aging on hematopoietic progenitor cells, blood and bone marrow from second- and third-trimester fetal, newborn, infant, adult, and aged rhesus monkeys (Macaca mulatta) were analyzed. CD34(+) cells were immunoselected and stained with propidium iodide for cell cycle analysis. Blood and bone marrow mononuclear cells were plated in methylcellulose, and erythroid and myeloid progenitors were grown and counted. A higher frequency of circulating CD34(+)CD38(-) and CD34(+)DR(-) cells was observed in second-trimester fetuses compared with the other age groups. The frequency of bone marrow CD34(+)CD38(-) and CD34(+)DR(-) cells declined in adult and aged animals when compared with the younger age groups. Cell-cycle analysis showed 4.5% second-trimester fetal bone marrow CD34(+) cells entering the G(2)/M phase, compared with 1.7% CD34(+) cells in aged animals. More than 95% of circulating CD34(+) cells remained quiescent for most age groups, except for second-trimester fetuses. Adult marrow myeloid progenitors were found in a lower quantity when compared with third-trimester fetuses, whereas erythroid progenitors were greatest in early-gestation fetuses and adults. The results of these studies suggest that 1) the greatest quantity of CD34(+)CD38(-) and CD34(+)DR(-) cells was found in fetal and infant bone marrow, 2) the frequency of cycling CD34(+) cells declines with maturation and aging, and 3) an age-dependent difference in lineage commitment occurs.

Characterization of restrictions to human immunodeficiency virus type 1 infection of monocytes

Tissue macrophages are an important cellular reservoir for replication of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus. In vitro, the ability of macrophages to support viral replication is differentiation dependent in that precursor monocytes are refractory to infection. There is, however, no consensus as to the exact point at which infection is restricted in monocytes. We have revisited this issue and have compared the efficiencies of early HIV-1 replication events in monocytes and in differentiated macrophages. Although virus entry in monocytes was comparable to that in differentiated macrophages, synthesis of full-length viral cDNAs was very inefficient. Relative to differentiated macrophages, monocytes contained low levels of dTTP due to low thymidine phosphorylase activity. Exogenous addition of D-thymidine increased dTTP levels to that in differentiated macrophages but did not correct the reverse transcription defect. These results point to a restriction in monocytes that is independent of reverse transcription precursors and suggest that differentiation-dependent cellular cofactors of reverse transcription are rate limiting in monocytes.

Flow cytometric analysis of PKH26-labeled goldfish kidney-derived macrophages

We recently demonstrated that a goldfish macrophage cell line (GMCL) and primary in vitro-derived kidney macrophage (IVDKM) cultures contain three distinct macrophage subpopulations. Morphological, cytochemical, functional, and flow cytometric characterization of these sub-populations suggested that they may represent cells of the macrophage lineage temporally arrested at distinct differentiation junctures of fish macrophage development (putative early progenitors, monocytes, and macrophages). In this study, we examined the proliferation and differentiation events leading to the generation of mature macrophage-like cells from goldfish kidney hematopoietic tissues. The flow cytometric studies were done after labeling macrophages with PKH26 fluorescent dye and analysis of the data using the MODFIT software. Our results showed that IVDKM cultures proliferated non-synchronously, suggesting the presence of a temporal control mechanism regulating the number of cells entering the paths towards maturation. Such control is most evident during early progenitor proliferation and differentiation events. Our results showed that proliferation may not be a requirement for differentiation of early progenitors to putative monocyte and macrophage subsets. Detailed observation of the mature macrophage-like subpopulation indicated that: 1) they appear to develop from both, the differentiation of monocyte-like cells, and direct differentiation of early progenitors in the absence of a monocyte-like stage; and (2) mature macrophage-like cells appeared to be capable of self-proliferation. Our results suggest the presence of alternate pathways of fish macrophage development other than the classical hematopoietic pathway.

Phenotypic and functional characterization of normal rat pleural macrophages in comparison with autologous peritoneal and alveolar macrophages

Pleural mononuclear phagocytes (PleMP) were isolated from normal rats by pleural lavage and compared with autologous peritoneal (PerMP) and bronchoalveolar mononuclear phagocytes (BAMP) isolated by peritoneal and bronchoalveolar lavage, respectively. The phagocytic activity of PleMP, PerMP, and BAMP, evaluated by testing their ability to ingest latex beads, was lower for PleMP and PerMP than for BAMP. The phenotype of PleMP, PerMP, and BAMP was characterized by immunocytochemical staining with a panel of monoclonal antibodies (mAbs). As expected, PleMP, PerMP, and BAMP did not react with OX19, OX33, ED5, MOM/3F12/F2, and anticytokeratin mAbs, specific for T lymphocytes, B lymphocytes, dendritic cells, granulocytes, and epithelial/mesothelial cells, respectively. Moreover, PleMP and PerMP populations were highly enriched with OX6-, OX42-, ED7-, and ED8-positive MP, whereas BAMP population was enriched with ED1- and ED9-positive cells. To test the ability of PleMP, PerMP, and BAMP to function as accessory cells (AC), mitomycin C-treated MP were used as stimulatory cells in mixed leukocyte reaction experiments, using allogeneic T cells as responders. 3HdTR incorporation by T cells was assessed as an index of AC function. PleMP and PerMP were more potent AC than BAMP. Moreover, when cultured together with autologous pulmonary interstitial dendritic cells, PleMP and PerMP exerted a more potent ability to stimulate T-cell proliferation than did BAMP. To investigate the capacity of MP to function as bactericidal and fungicidal cells, we tested their ability to kill Escherichia coli and Cryptococcus neoformans, respectively. PleMP and PerMP were less potent bactericidal and fungicidal cells than BAMP. The results of this study demonstrate that PleMP isolated from normal rat pleural space are functionally and phenotypically different from BAMP but similar to PerMP, and suggest that these cells might play an important role in cell-mediated immune reactions in the pleural space.

Bone marrow cell response following induction of acute inflammation in different strains of mice

The magnitude of the macrophage inflammatory response differs among inbred mouse strains. Mice of the A/J strain respond poorly to sterile inflammatory stimuli while those of the C57BL/6 strain show a strong response. Inflammatory macrophages found at the site of inflammation are the product of bone marrow (BM) myeloid stem cells. Mice of the A/J strain were found to have half the number of BM nucleated cells per femur than those of the C57BL/6 strain. The lower BM cellularity may be one reason for the poor macrophage inflammatory response observed in A/J mouse strain. Using A x B/B x A recombinant inbred mouse strains, we determined that the number of nucleated cells per femur found in normal mice was not a determining factor of the magnitude of the macrophage inflammatory response. One additional explanation for the poor macrophage inflammatory response in mice of the A/J strain is their deficiency in the C5 component of complement. Using a C5-sufficient A/J.C5 congenic strain, we have previously shown that the presence of C5 on the A/J background improved their inflammatory response. We compared A/J and A/J.C5 mouse strains to determine whether or not C5 had an impact on the BM cell response to inflammatory stimulus. The presence of C5 on the A/J background could contribute to the improvement of the inflammatory response in mice of the A/J.C5 strain by inducing a greater number of nucleated cells to exit the BM compartment early following induction of inflammation.

The magnitude of macrophage inflammatory response does not directly depend on ability of bone marrow cells to respond to interleukin-3 in mice of different strains

The multicolony stimulating factor Interleukin-3 (IL-3) has a role in regulating the proliferation, differentiation, and survival of myeloid stem cells and committed progenitor cells within each of the myeloid lineages. It has been referred to as an emergency factor appearing following triggering of an inflammatory response. The ability of bone marrow (BM) stem cells to respond to a stimulus such as IL-3 in vitro may reflect the in vivo capacity of BM stem cells to generate newly BM-derived macrophages being recruited to an inflammatory site. Both parameters, namely the BM cell response to in vitro IL-3 treatment and the magnitude of the macrophage inflammatory response vary among inbred mouse strains. Mice of the A/J strain are known to have weak macrophage inflammatory response to a phlogistic agent and their BM cells are hyporesponsive to IL-3 exposure. In contrast, mice of the C57BL/6 strain mount a high macrophage inflammatory reaction to a stimulus, and their BM cells strongly proliferate in response to the presence of IL-3. Thus, we examined whether or not the type of BM cell response to IL-3 (i.e., A/J- or C57BL/6-like) determines the magnitude of the macrophage inflammatory response using the A x B/B x A recombinant inbred (RI) mouse strain system. The two traits were found not to cosegregate, suggesting that they are not linked. The continuous strain distribution pattern of the magnitude of the macrophage inflammatory response obtained in mice of the A x B/B x A RI strains implies that this trait is under the control of several genes.

Cytokine-induced differentiation of cultured nonadherent macrophages

Monocytes were isolated from peripheral blood and cultured in vitro for more than 3 weeks in glass chamber slides. Phenotypically and ultrastructurally these nonadherent macrophages (NAM) appear similar to connective tissue resident macrophages. They constitutively secrete a high amount of IL-1ra and little or no IL-1 alpha or IL-1 beta. When exposed to GM-CSF, IL-2, or IFN-gamma for 24 hr, NAM become adherent and undergo dramatic morphological changes. Cytokines treatment primes NAM for increased LPS-mediated TNF production and these GM-CSF- and LPS-treated NAM are cytotoxic to WEHI 164, a TNF-sensitive target. Morphological changes and TNF production are both inhibited by antimetabolites and a variety of antineoplastic drugs. Although morphology inhibition is reversible under certain circumstances, inhibition of TNF synthesis is irreversible. These findings suggest that cytokines might play a role in differentiation and maturation of long-term cultured monocytes. Furthermore, the effects of antimetabolites and antineoplastic drugs on arresting the differentiation processes may significantly impair antitumor functions of macrophages.

Class II major histocompatibility complex antigen expression on unstimulated and gamma-interferon stimulated monocytes from patients with multiple sclerosis, rheumatoid arthritis and normal controls

HLA-DR, HLA-DQ, and HLA-DP antigen expression was assessed by immunofluorescent flow cytometry on monocytes from 19 patients with active multiple sclerosis (MS), 19 with inactive MS, 7 patients with early active rheumatoid arthritis (RA), and 19 normal controls. Percentage positivity and median channel fluorescence (MCF) were determined after separation of the monocytes (TO) and following 48 h culture with (T48 + IFN) and without (T48) recombinant gamma interferon (rIFN-gamma). The percentage positivity of the cells was normal at TO for all groups of patients for each of the HLA types but statistically significantly increased above normal, on monocytes from patients with inactive MS, after culture with rIFN-gamma. At TO, the MCF values for HLA-DQ, and HLA-DP were statistically significantly increased above normal on monocytes from patients with active MS indicating some pre-programming of the cells in vivo. After culture, when the carry-over from baseline TO values was eliminated, the increment in MCF for HLA-DR, on monocytes from patients with inactive MS, was statistically significantly lower than normal in the non-gamma-IFN cultures but was normal in the presence of rIFN-gamma. Conversely, the increment in MCF for HLA-DP on monocytes from patients with active MS was significantly lower than normal after culture with rIFN-gamma. Therefore, the stimulation required to increase antigen density on cells already expressing antigen may be different to that required to stimulate de novo expression on negative cells. Both systems appear to be abnormal in MS, possibly reflecting differences in disease activity, while only one system appears abnormal in RA.

Reduction of monocyte 5'nucleotidase activity by gamma-interferon in multiple sclerosis and autoimmune diseases

Ecto-5'nucleotidase (5'NT) activity in the plasma membrane of peripheral blood monocytes from patients with multiple sclerosis (MS), rheumatoid arthritis (RA), myasthenia gravis (MG), motor neuron disease (MND), and from normal control subjects of similar age was determined by radioisotopic assay. The activity in unstimulated monocytes cultured for 24 and 48 hours was found to be higher than normal in 56% of patients with active relapsing MS, 29% of patients with RA, and 7% of patients in the MG/MND group. While the enzyme activity was reduced after cultivation of the cells with recombinant interferon-gamma (gamma-IFN) in all of the groups studied, the percentage reduction was significantly greater in monocytes from patients with active relapsing MS who were in relapse at the time of sampling (p = 0.03). HLA-DR expression was monitored using immunofluorescence staining with monoclonal antibody and showed that similar numbers of monocytes in all patient and control groups expressed this antigen. Thus, while high monocyte 5'NT activity was found principally in patients with active relapsing MS and in some patients with RA, the monocytes from patients with MS were, in addition, exquisitely sensitive to stimulation with gamma-IFN.

Modulation of the immune response to Listeria monocytogenes by benzene inhalation

Benzene is a potent bone marrow toxicant. While all blood cell types are targets for benzene poisoning, lymphocytes are particularly sensitive. The immunotoxic consequences of benzene or its metabolites have been demonstrated in a number of in vitro studies; however, little data exist regarding the effects of benzene on host resistance to infectious agents. This investigation examined the effects of benzene on murine resistance to an infectious agent, Listeria monocytogenes. Four concentrations of benzene were employed, 10, 30, 100, and 300 ppm. To determine recovery from the effects of benzene, two exposure regimens were employed: 5 days prior to infection (preexposure), or 5 days prior to and 7 days during infection (continuous exposure). Appropriate air controls were maintained. Splenic bacterial counts and immune responsive cell populations were determined from mice killed at Days 1, 4, and 7 of infection. Preexposure to benzene produced increased bacterial numbers at Day 4 of the infection only at the highest benzene concentration (300 ppm). In contrast, continuous exposure produced increased bacterial numbers at Day 4 of infection at all but the lowest benzene concentration (10 ppm). Bacteria counts were not increased in any benzene-treated group at Day 1 or Day 7 of infection. The increased bacterial numbers at Day 4 suggest an effect on cell-mediated immune responses. Both T and B lymphocytes were particularly sensitive to benzene exhibiting reductions at all concentrations greater than or equal to 30 ppm for both exposure regimens. Esterase-positive cells, however, were relatively resistant to benzenes effects. The results point to a benzene-induced delay in the immune response to L. monocytogenes.

Human monocyte adherence measured by the nylon fibre microcolumn technique

A simple rapid method for the measurement of human monocyte adherence using nylon fibre microcolumns is described. The kinetics indicate the optimal contact time to be 30 min for monocytes, compared with 10 min for neutrophils. The optimal temperature is 37 degrees C; significantly low values were obtained for 4 degrees C and 45 degrees C, while intermediate values were obtained for 25 degrees C. Monocyte adherence was more sensitive to inhibition by fluoride than cyanide, suggesting that energy for adherence is mainly derived from the glycolytic pathway. The addition of phorbol myristate acetate enhances monocyte adherence. Significant decay in monocyte adherence occurred after isolation from whole blood for 24 h or longer.

Role of iron in intracellular growth of Trypanosoma cruzi

Host hypoferremic responses occur during infection with Trypanosoma cruzi, presumably through the transfer of iron to the sites of intracellular parasite replication. Depletion of host intracellular iron stores reduces parasite pathogenicity. It has therefore been hypothesized that T. cruzi requires iron for optimal growth in host cells and that, unlike extracellular pathogens, T. cruzi may benefit from host hypoferremic responses. These hypotheses were examined by the in vitro infection of peritoneal macrophages with T. cruzi. Various doses of desferrioxamine or referrated desferrioxamine were added to the culture medium, and parasite growth was monitored. The influence of treatment on uninfected macrophage morphology, function, and iron content was also verified. Desferrioxamine reduced the rate of amastigote replication in a dose-dependent fashion, whereas referrated desferrioxamine did not. The iron content of desferrioxamine-treated macrophages was decreased by 55% without provoking significant morphological or functional changes. Thus, amastigotes used host cell iron stores for optimal growth, and desferrioxamine reduced growth by depleting host cell iron. Hence, it was suggested that depletion of host intracellular iron stores may protect against T. cruzi and, furthermore, that host responses which transfer iron to the intracellular sites of T. cruzi replication may enhance parasite pathogenicity.