Colony-forming cells and colony-stimulating activity during listeriosis in genetically resistant or susceptible mice

Diminished hematopoietic activity associated with alterations in innate and adaptive immunity in a mouse model of human monocytic ehrlichiosis

Human monocytic ehrlichiosis (HME) is a tick-borne disease caused by Ehrlichia chaffeensis. Patients exhibit diagnostically important hematological changes, including anemia and thrombocytopenia, although the basis of the abnormalities is unknown. To begin to understand these changes, we used a mouse model of ehrlichiosis to determine whether the observed hematological changes induced by infection are associated with altered hematopoietic activity. Infection with Ehrlichia muris, a pathogen closely related to E. chaffeensis, resulted in anemia, thrombocytopenia, and a marked reduction in bone marrow cellularity. CFU assays, conducted on days 10 and 15 postinfection, revealed a striking decrease in multipotential myeloid and erythroid progenitors. These changes were accompanied by an increase in the frequency of immature granulocytes in the bone marrow and a decrease in the frequency of B lymphocytes. Equally striking changes were observed in spleen cellularity and architecture, and infected mice exhibited extensive extramedullary hematopoiesis. Splenomegaly, a characteristic feature of E. muris infection, was associated with an expanded and disorganized marginal zone and a nearly 66-fold increase in the level of Ter119(+) erythroid cells, indicative of splenic erythropoiesis. We hypothesize that inflammation associated with ehrlichia infection suppresses bone marrow function, induces the emigration of B cells, and establishes hematopoietic activity in the spleen. We propose that these changes, which may be essential for providing the innate and acquired immune cells to fight infection, are also responsible in part for blood cytopenias and other clinical features of HME.

Prophylactic administration of Withania somnifera extract increases host resistance in Listeria monocytogenes infected mice

In this study, we demonstrated that Withania somnifera L. extract (WSE) protects mice from a lethal dose of Listeria monocytogenes when administered prophylactically at 100, 250 and 500 mg/kg for 10 days, with survival rates up to 30%. These doses also prevented the myelosuppression and the splenomegaly caused by a sublethal infection with L. monocytogenes, due to increased numbers of granulocyte-macrophage progenitors (CFU-GM) in the bone marrow. Investigation of the production of colony-stimulating factors (CSFs) revealed increased colony-stimulating activity (CSA) in the serum of normal and infected mice pre-treated with WSE. Further studies to investigate the levels of interferon-gamma (INF-gamma) and lymphocyte cell proliferation were undertaken. We observed dose-dependent increases in cell proliferation and in the levels of INF-gamma in mice infected with L. monocytogenes and treated with WSE. All together, our results suggest that WSE indirectly modulates immune activity and probably disengages Listeria-induced suppression of these responses by inducing a higher reserve of myeloid progenitors in the bone marrow, proliferation of lymphocytes and increased INF-gamma levels.

Uncaria tomentosa extract increases the number of myeloid progenitor cells in the bone marrow of mice infected with Listeria monocytogenes

In this study, we demonstrated that Uncaria tomentosa extract (UTE) protects mice from a lethal dose of Listeria monocytogenes when administered prophylactically at 50, 100, 150 and 200 mg/kg for 7 days, with survival rates up to 35%. These doses also prevented the myelosuppression and the splenomegaly caused by a sublethal infection with L. monocytogenes, due to increased numbers of granulocyte-macrophage progenitors (CFU-GM) in the bone marrow. Non-infected mice treated with 100 mg/kg UTE also presented higher numbers of CFU-GM in the bone marrow than the controls. Investigation of the production of colony-stimulating factors revealed increased colony-stimulating activity (CSA) in the serum of normal and infected mice pre-treated with UTE. Moreover, stimulation of myelopoiesis and CSA occurred in a dose-dependent manner, a plateaux being reached with the dose of 100 mg/kg. Further studies to investigate the levels of factors such as IL-1 and IL-6 were undertaken. We observed increases in the levels of IL-1 and IL-6 in mice infected with L. monocytogenes and treated with 100 mg/kg of UTE. White blood cells (WBC) and differential counting were also performed, and our results demonstrated no significant changes in these data, when infected mice were pre-treated with 100 mg/kg of UTE. All together, our results suggest that UTE indirectly modulates immune activity and probably disengages Listeria-induced supression of these responses by inducing a higher reserve of myeloid progenitors in the bone marrow in consequence of biologically active cytokine release (CSFs, IL-1 and IL-6).

Stromal Cells Direct Local Differentiation of Regulatory Dendritic Cells

CD11c(hi) dendritic cells (DC) play an essential role during the initiation of cell-mediated immunity. Recently, CD11c(lo)CD45RB(hi) DC with regulatory properties have been described. However, the origins of regulatory DC are poorly understood. Here, we show that spleen-derived stromal cells promote selective development of CD11c(lo)CD45RB(+) IL-10-producing regulatory DC from lineage-negative c-kit(+) progenitor cells. These DC have the capacity to suppress T cell responses and induce IL-10-producing regulatory T cells in vitro and to induce antigen-specific tolerance in vivo. Furthermore, stromal cells from mice infected with Leishmania donovani more effectively supported differentiation of these highly potent regulatory DC. The ability of tissue stromal cells to direct the development of DC with a regulatory phenotype thus provides a new mechanism for local immune regulation.

Bone marrow colony-formation in vitro after infection of genetically defined inbred mice with Candida albicans

The effect of C. albicans infection on the production of haematopoietic precursor cells in the bone marrow of CBA/CaH and BALB/c mice was evaluated by assay of colony formation in vitro. In immunocompetent mice, neither systemic nor oral infection induced significant alterations in colony formation by bone marrow from the two mouse strains, and Candida infection did not alter the proportion of morphological cell types in the colonies. However, the number of neutrophil-like was relatively greater in colonies derived from acutely infected CBA/CaH nude mice than in those from BALB/c nude mice, whereas small mononuclear cells were present in higher proportions in the latter strain. In both strains of nude mice, there was an increase in colony formation at 6 days after oral infection, but at 8 weeks, when the infection had become chronic, the production of bone marrow cells by CBA/CaH nude mice was significantly less than that by BALB/c nude mice. Reconstitution of nude mice with syngeneic lymphocytes enhanced the production of bone marrow precursor cells by BALB/c, but not by CBA/CaH mice, suggesting that T cells can enhance host resistance by promoting the colony-forming response of the bone marrow in BALB/c mice that are genetically resistant to tissue damage, but not in CBA/CaH that are prone to severe lesions. Finally, culture with Candida antigen in vitro decreased the number of colony-forming cells in cultures from CBA/CaH, but not from BALB/c mice.

Evaluation of Caesalpinia ferrea extract on bone marrow hematopoiesis in the murine models of listeriosis and Ehrlich ascites tumor

The capacity of hematopoietic tissues to produce and mobilize phagocytes to the site of infection and tumor growth is of central importance to mediate the early immunological response. In this perspective, studies from our laboratory have defined Listeria monocytogenes infection and the Ehrlich ascites tumor (EAT) as useful models to investigate the effects of natural compounds on the growth and differentiation of granulocyte-macrophage progenitor cells (CFU-GM). As expected, a significant reduction in the number of bone marrow CFU-GM was observed in the initial stages of infection with a sublethal dose of Listeria. Similarly, the bone marrow CFU-GM decreased sharply 4 days after the EAT transplantation. Treatment of infected and tumor-bearing mice with 500 and 1,000 mg/kg of Caesalpinia ferrea aqueous extract, given 3 times orally, significantly stimulated myelopoiesis, whereas no effects were observed with the 250 mg/kg dose. Similar results were obtained in normal mice. The administration of the two higher doses of the extract also protected 15-20% of mice from a lethal dose of Listeria and significantly prolonged survival of EAT-bearing mice. In summary, these results demonstrate that C. ferrea extract acts as a positive regulator of myelopoiesis, and suggest that the therapeutic effect of C. ferrea may be partially mediated by this action.

Adjuvant effect of Pluchea quitoc extract on the resistance of tumor-bearing mice by modulation of the host hematopoietic response

Progressive tumor growth is regularly accompanied by changes in the cellular constituents of the immune system. Evidence suggests that soluble factors generated during tumor growth can affect the amount of granulocyte-macrophage progenitors. In vitro colony growth of progenitor cells may be an early indicator of the cellular changes associated with tumor growth. Pluchea quitoc has been previously found to modulate the hematopoietic response during bacterial infection. This study was designed to investigate the effects of P. quitoc on the growth and differentiation of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) in Ehrlich ascites tumor-bearing mice. In contrast to the myelosuppression developed in the tumor-bearing animals, treatment with P. quitoc ethanolic extract (250, 500 or 1000 mg/kg) for 3 consecutive days after tumor challenge reversibly stimulated myelopoiesis, restoring the number of CFU-GM to normal. This same dose-schedule also increased colony formation in normal mice as compared to controls. In addi tion, P. quitoc significantly enhanced survival of tumor-bearing mice. These results suggest an immunoregulatory role for P. quitoc in counteracting the tumor-induced myelopoietic suppression as well as usefulness as adjuvant treatment of cancer.

Stimulation of myelopoiesis in Listeria monocytogenes-infected mice by an aggregated polymer isolated from Aspergillus oryzae

In this work, we investigated the effects of the proteic aggregated polymer of magnesium ammonium phospholinoleate-palmitoleate anhydride (MAPA) isolated from Aspergillus oryzae on the growth and differentiation of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) in Listeriamonocytogenes-infected mice. A significant reduction in the CFU-GM number was observed in the initial phase of infection with a sublethal dose of Listeria. Treatment of mice with 0.5, 2.0 and 5.0 mg/kg MAPA for 7 days prior to infection significantly stimulated myelopoiesis in a dose-dependent manner. Moreover, treatment with 0.5 and 5.0 mg/kg MAPA resulted in 30% and 40% cures of mice lethally infected with Listeria, respectively. MAPA added directly to the culture dishes hardly affected colony formation by bone marrow cells, suggesting an indirect effect ofthis compound on myelopoiesis in vivo. In summary, the data show that MAPA can modulate the CFU-GM generation and antibacterial resistance in listeriosis. As the ability of hematopoietic tissues to produce phagocytes is of particular significance to mediate resistance to Listeria, the promotion of bone marrow CFU-GM by MAPA may contribute to a rapid restoration of phagocyte numbers in infected sites, thus mitigating the course of infection.

Stimulatory action of Pluchea quitoc extract on the hematopoietic response during murine listeriosis

The importance of both granulocytes and macrophages in the response to Listeria monocytogenes infection make this infection a suitable choice to investigate the effects of Pluchea quitoc on hematopoiesis. A significant depletion of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) was observed at 48 and 72 h after intraperitoneal infection of mice with 1 x 10(4) L. monocytogenes. However, the treatment of infected animals with P. quitoc ethanolic extract (250, 500 or 1000 mg/kg) given orally for 3 consecutive days prior to infection produced a stimulatory effect on myelopoiesis, restoring the number of CFU-GM to normal. This same dose-schedule also increased colony formation in normal mice as compared to controls. In addition, P. quitoc significantly enhanced survival of infected mice. Thus, it is probable that the ability of P. quitoc to induce a higher reserve of granulocyte-macrophage precursors in the bone marrow is of major significance in determining early resistance to infection.

Enhanced hematopoietic activity accompanies parasite expansion in the spleen and bone marrow of mice infected with Leishmania donovani

In this study, we have analyzed hematopoietic activity in the spleen, bone marrow, and blood of BALB/c and scid mice infected with Leishmania donovani. Our analysis demonstrates that infection induces a rapid but transient mobilization of progenitor cells into the circulation, associated with elevated levels of granulocyte/macrophage colony-stimulating factor (GM-CSF) and MIP-1alpha. From 14 to 28 days postinfection, when parasite expansion begins in the spleen and bone marrow, both the frequency and cell cycle activity of hematopoietic progenitors, particulary CFU-granulocyte, monocyte, are dramatically increased in these organs. This is associated with increased accumulation of mRNA for GM-CSF, M-CSF, and G-CSF, but not interleukin-3. Our data also illustrate that hematopoietic activity, as assessed by changes in the frequency of progenitor cell populations and their levels of cell cycle activity, can be regulated in both a T-cell-independent and T-cell-dependent, as well as in an organ-specific, manner. Collectively, these data add to our knowledge of the long-term changes which occur in organs in which L. donovani is able to persist.

Haemopoiesis in mice genetically lacking granulocyte-macrophage colony stimulating factor during chronic infection with Mycobacterium avium

In order to test the role of granulocyte-macrophage colony stimulating factor (GM-CSF) in haemopoiesis during chronic infection, mice with a targeted disruption of the gene for GM-CSF were infected intraperitoneally with the facultative intracellular pathogen, Mycobacterium avium. The bacteria spread to lungs, liver and spleen and persisted for more than 10 weeks at levels between 105 and 106 CFU. Bacterial numbers did not differ significantly between infected GM-CSF-/- and wild-type mice, making this an excellent model in which to study the effects of GM-CSF deficiency on haemopoietic cells without complications of interpretation relating to differences in bacterial load. Haemopoietic colony forming cells (CFC) in the bone marrow of GM-CSF-/- mice before infection were not different from wild-type. However, whereas CFC in wild-type mice increased 1.5-fold with infection, GM-CSF-/- mice were unable to increase their CFC and numbers were significantly lower than in infected wild-type mice. Cells attracted to the peritoneal cavity of the GM-CSF-/- mice following i.p. injection of bacteria were notably lacking in the large, granular macrophages of activated appearance, which were a feature in wild-type mice. Nitric oxide production by peritoneal cells from GM-CSF-/- mice was deficient. Thus, GM-CSF is not critical for haemopoiesis during chronic infection, but in its absence the mice are unable to increase their output of haemopoietic cells and there are deficiencies in macrophage activation.

Effects of Chlorella vulgaris on bone marrow progenitor cells of mice infected with Listeria monocytogenes

In this study we investigated the effects of the treatment with Chlorella vulgaris extract (CVE) on the hematopoietic response of granulocyte-macrophage colony-forming unit (CFU-GM) of mice infected with a sublethal dose of Listeria monocytogenes (1 x 10(4) organisms/animal). CVE was given orally as 50 mg/kg/day for 5 days. In the CVE treated/infected groups L. monocytogenes was administered at the end of CVE treatment. The colony stimulating activity of the serum (CSA) was also studied in all groups. Although no effects on CFU-GM, as compared to controls, were observed in the groups receiving CVE alone, the extract produced an increase in CSA levels as compared to controls. On the other hand, the presence of the infection led to a significant reduction in the numbers of CFU-GM as observed at 48 and 72 h after the infection, in spite of the significant increase in serum CSA activity. CVE treatment of infected animals restored the numbers of CFU-GM to control levels. In the treated/ infected group the increased serum CSA was significantly higher than that observed in the only infected group. The CVE treatment (50 and 500 mg/kg) of mice infected with a dose of 3 x 10(5) bacteria/animal, which was lethal for all the non-treated controls, produced a dose-response protection which led to a 20 and 52% survival, respectively. These results demonstrated that CVE produces a significant increase in the resistance of the animals infected with L. monocytogenes, and that this protection is due, at least in part, to increased CFU-GM in the bone marrow of infected animals.

Bone marrow cellular composition in Listeria monocytogenes infected mice detected using ER-MP12 and ER-MP20 antibodies: a flow cytometric alternative to differential counting

Detailed assessment of bone marrow cellular composition is essential in the evaluation of various experimental in vivo systems, such as expression of transgenes, null mutations and stimulation of host defence in infection. Traditional morphological analysis of mouse bone marrow is laborious, requires specific cytological expertise, and is somewhat subjective. As an alternative, we have examined whether double labelling of bone marrow with the anti-precursor monoclonal antibodies ER-MP12 and ER-MP20 could be used for differential analysis by flow cytometry, as these antibodies define six relatively homogeneous cell populations in mouse bone marrow. Following a sublethal infection of mice with Listeria monocytogenes, we monitored changes in cellular composition of the bone marrow at various time points in three ways: differential morphological count; single-color flow cytometric analysis using markers for the myeloid, erythroid and lymphoid lineages; and double labelling with ER-MP12 and ER-MP20. As expected, the bone marrow composition changed dramatically during infection, leading to an increase of myeloid cells which peaked after 1 week of infection. Data determined by ER-MP12/20 flow cytometric analysis appeared to be in close agreement with both morphology and lineage marker analysis. In addition, ER-MP12/20 analysis provided more detailed information with regards to the presence of early myeloid precursors compared to lineage marker analysis. These data show that flow cytometric analysis of bone marrow using ER-MP12 and ER-MP20 monoclonal antibodies provides a relatively simple, rapid and objective assay when evaluating cellular composition in the bone marrow of the mouse.

Essential Roles for Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and G-CSF in the Sustained Hematopoietic Response ofListeria monocytogenes–Infected Mice

The in vivo roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte (G)-CSF were studied in factor-deficient gene-targeted knockout mice infected with the facultative intracellular bacterium Listeria monocytogenes.Previous results showed that G-CSF−/− mice had an underlying selective deficiency in granulopoiesis, but GM-CSF−/− mice had little disturbance in resting hematopoiesis. Nevertheless, in this study it is revealed that 3 days after intraperitoneal infection with 2 × 105Listeria, GM-CSF−/− mice harbored 50-fold more organisms in their spleen and liver than similarly infected wild-type mice. This was accompanied by a severe depletion of bone marrow hematopoietic cells and a deficient inflammatory response in their peritoneal cavity. Thus, GM-CSF is essential for emergency, but not resting, hematopoiesis. In contrast, G-CSF−/− mice were markedly susceptible to low doses (2 × 104) ofListeria intraperitoneally. After infection, the acute (1 day) granulocyte infiltration to the peritoneal cavity was normal compared with wild type, but the more prolonged monocyte response was deficient, reflecting a continued decrease in bone marrow cellularity and hematopoiesis over 3 days, which was not observed in infected wild-type mice. It is thus apparent that G-CSF deficiency affects monocytopoiesis as well as granulopoiesis during infection.

Essential Roles for Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and G-CSF in the Sustained Hematopoietic Response ofListeria monocytogenes–Infected Mice

The in vivo roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte (G)-CSF were studied in factor-deficient gene-targeted knockout mice infected with the facultative intracellular bacterium Listeria monocytogenes.Previous results showed that G-CSF−/− mice had an underlying selective deficiency in granulopoiesis, but GM-CSF−/− mice had little disturbance in resting hematopoiesis. Nevertheless, in this study it is revealed that 3 days after intraperitoneal infection with 2 × 105Listeria, GM-CSF−/− mice harbored 50-fold more organisms in their spleen and liver than similarly infected wild-type mice. This was accompanied by a severe depletion of bone marrow hematopoietic cells and a deficient inflammatory response in their peritoneal cavity. Thus, GM-CSF is essential for emergency, but not resting, hematopoiesis. In contrast, G-CSF−/− mice were markedly susceptible to low doses (2 × 104) ofListeria intraperitoneally. After infection, the acute (1 day) granulocyte infiltration to the peritoneal cavity was normal compared with wild type, but the more prolonged monocyte response was deficient, reflecting a continued decrease in bone marrow cellularity and hematopoiesis over 3 days, which was not observed in infected wild-type mice. It is thus apparent that G-CSF deficiency affects monocytopoiesis as well as granulopoiesis during infection.

Listeria monocytogenes in laboratory mice: a model of short-term infectious and pathogenic processes controllable by regulated protective immune responses

The mammalian immune system is an integrated network of tissue, leukocytes and effector and regulatory molecules. All these components operate i) to maintain the proper structure of and processes expressed by each tissue. and ii) to protect the hosts from those microorganisms that generally invade them as part of their life cycle. Among the invading microorganisms. Listeria monocytogenes (L. monocytogenes) can persist as a live organism independent of the host, and is, thus, able to drive short-term infectious and pathogenic processes that are controlled by integrated innate and adaptive protective immune responses driven by CD8 and CD4 type 1 T lymphocytes acting on non-T non-B leukocytes. Although the effector functions and the fine specificity of T lymphocytes have been more and more characterized, an understanding of the precise regulation of both leukocyte traffic and T-lymphocyte migration depends on knowledge of the early tissue distribution of L. monocytogenes, points that are addressed in this review.

Differential regulation of cytokine and cytokine receptor mRNA expression upon infection of bone marrow-derived macrophages with Listeria monocytogenes

Cytokine and cytokine receptor mRNA expression was analyzed by PCR-assisted amplification of RNA extracted from bone marrow-derived macrophages (BMM phi) at different time points after infection with Listeria monocytogenes. The mRNAs for the cytokines interleukin-1 alpha (IL-1 alpha), IL-1 beta, and tumor necrosis factor alpha (TNF-alpha) were induced early after infection, whereas IL-6 mRNA appeared later and even nonhemolytic Listeria strains, which are unable to grow inside eukaryotic cells, induced the same cytokine mRNAs at levels similar to those of the wild-type strain. In most cases, the amounts of cytokines determined by various bioassays correlated with the level of mRNA induction. Inhibition of phagocytic uptake of L. monocytogenes by cytochalasin D treatment resulted in adherent bacteria which still induced the proinflammatory cytokines. In BMM phi, the level of IL-1 receptor II mRNA was unaffected, whereas mRNA expression of the two subtypes of tumor necrosis factor receptors (TNF-RI and TNF-RII) was differentially regulated upon infection: transcription of TNF-RI was reduced, and that of TNF-RII mRNA was induced. Similar to the decreased TNF-RI mRNA expression, gamma interferon receptor mRNA was downregulated in L. monocytogenes-infected BMM phi. This dose- and time-dependent induction or downregulation of cytokine receptor mRNA following L. monocytogenes infection of BMM phi was not observed upon infection of established macrophage-like cell lines J774 and P388D1. Induction of IL-6 mRNA as well as IL-1 alpha/beta and TNF-alpha mRNAs upon L. monocytogenes infection of BMM phi occurs independently of autocrine TNF-alpha signaling via TNF-RI or TNF-RII, as shown by infection of TNF-RI- and TNF-RII-deficient macrophages derived from mutant B6 x 129 mice. In contrast to gamma interferon receptor mRNA, both TNF receptor subtype mRNAs were not influenced by L. monocytogenes infection of hybrid (B6 x 129) mouse macrophages. Whereas the proinflammatory cytokine mRNAs were even induced after infection with the nonpathogenic species L. innocua, no alteration of cytokine receptor mRNA expression was observed after challenge of BMM phi with this nonpathogenic species, suggesting that the modulation of cytokine and cytokine receptor expression by L. monocytogenes could be an important way of inhibition of macrophage stimulation.

Effect of genetic variation on induced neutrophilia in mice

Mice from a variety of strains were injected with a sterile irritant (Brewer's thioglycolate) and killed bacteria (Staphylococcus aureus, Staphylococcus epidermidis, or Escherichia coli) to determine their effect on accumulation of neutrophils in the peritoneal cavity. Peak accumulation occurred around 15 h postinjection and showed significant strain-related variation. C57BL/10 mice were identified as having a high-responder phenotype and BALB/c mice a low-responder phenotype. Inheritance of the high-responder phenotype followed simple Mendelian genetics: (BALB/c x C57BL/10)F1 mice were found to be more responsive than either parental phenotype. Major histocompatibility complex H-2d haplotype was found to convey an augmented neutrophil response in conjunction with B10 background high-responder genes (B10.D2/n) but the H-2d haplotype per se was not the only factor in determining high responsiveness. Gram-positive and gram-negative bacteria appeared to activate different immune mechanisms. Both gram-negative bacteria and lipopolysaccharides (LPS) induced a response similar to, but less potent than, that induced by Brewer's thioglycollate. Neutralization of the LPS content of Brewer's thioglycolate abrogated the response.

The role of cytokines in experimental listeriosis

Listeria monocytogenes is a Gram-positive, intracytoplasmatically replicating pathogen that elicits host reactions which are very similar in man and rodents. Using murine listeriosis as a highly reproducible and convenient experimental model for studying the immune response to infections with facultative intracellular bacteria, Mackaness developed the concept of T cell-mediated macrophage activation as the pivotal mechanism in host defense against this type of infectious agents. Continued research in listeriosis itself, however, provided paradoxical findings that challenged the original dogma. In particular, the finding that T cell-mediated inflammatory events, like DTH and granuloma formation, can be dissociated from protective effector mechanisms has provided a new impetus and experimental access to characterizing the molecular mediators responsible for these diverging phenomena. This review first summarizes the cellular basis for the dichotomy of immunological phenomena outlined above and will then relate recent findings on cytokine expression in infected tissues to these dual categories of the host response to infection. The authors will focus on data obtained from in vivo experiments and draw on evidence from in vitro systems only when appropriate in vivo verification is still lacking. The data presented will cover the developments made in the field of cytokine research since our previous review in 1981 (Rev. Infect. Dis. 3: 1221-1250). Detectable numbers of listeria-specific T cells become apparent on day 4 to 5 of a primary infection. Whereas the localized and sustained release of TNF and IFN-gamma mediated by CD4+ cells seems to be the focusing event triggering mononuclear cell accumulation, the coincidental eradication of bacteria critically depends on CD8+ and/or CD4-CD8-Thy1+ cells. Their effector functions, however, remain obscure, since cytokines cannot be identified that will substitute for their presence. None of the cytokines studied thus far has been demonstrated to effectively cure an established infection. In addition, the increased production of cytokines characteristic of an anamnestic response (IL-2, IL-3, IL-4, IFN-gamma and TNF) can be dramatically reduced by depleting CD4+ T cells without any effect on the animal's ability to eradicate high lethal doses of bacteria and Listeria-specific CD8+ T cells can mediate protection even in the presence of neutralizing antibodies to IFN-gamma. In conclusion, the murine model of Listeria infection provides an interesting experimental approach for the development of immunotherapeutic strategies aimed at reducing T cell-mediated immunopathology without interfering with innate resistance and T cell-mediated cure and prevention of disease.

Analysis of cytokine mRNA expression in Listeria-resistant C57BL/6 and Listeria-susceptible A/J mice during Listeria monocytogenes infection

This laboratory previously reported that mRNA expression for many cytokines, as determined by reverse transcription-polymerase chain reaction analysis, is induced rapidly in the spleen during murine listeriosis. In the present study, the patterns of cytokine mRNA expression in spleens and livers of Listeria-resistant C57BL/6 and Listeria-susceptible A/J mice were compared. In addition, in situ hybridization was performed to evaluate the distributions of cytokine mRNA-expressing cells in these tissues. Listeria-resistant C57BL/6 mice demonstrated greater expression of gamma interferon (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNAs in the spleen than Listeria-susceptible A/J mice. Greater numbers of cells expressing IFN-gamma and GM-CSF mRNAs were observed by in situ hybridization in the spleens of C57BL/6 mice than in those of A/J mice. C57BL/6 and A/J mice did not differ in their expression of IFN-gamma mRNA in the liver. Nor did C57BL/6 and A/J mice differ in their expression of tumor necrosis factor alpha, interleukin-1 alpha (IL-1 alpha), IL-2, IL-4, or IL-6 mRNA in the liver or spleen, as determined by reverse transcription-polymerase chain reaction and in situ hybridization. These results indicate that the greater resistance of C57BL/6 mice to Listeria monocytogenes infection is associated with greater expression of IFN-gamma and GM-CSF mRNAs in the spleen and GM-CSF mRNA in the liver.

Interleukin-6 production during chronic experimental infection

The appearance of interleukin-6 (IL-6) in serum of mice was monitored during the course of chronic infection with either Brucella abortus vaccine strain 19 or a virulent Mycobacterium avium Complex (MAC) isolate. Serum IL-6 during brucella infection was higher than during infection with MAC, despite similar numbers of bacteria. Furthermore, IL-6 titres decreased after the peak of infection, falling to baseline levels before these chronic infections were eradicated. The ability of peritoneal cells or spleen cell suspensions to produce IL-6 under either specific or non-specific stimulus was greatly enhanced by infection. While production of IL-6 by these cultures was apparently mostly independent of T cells, T cells from infected mice could produce an IL-6 response. Thus CD4+ T lymphocytes prepared from mice which had recovered from B. abortus infection, cultured with antigen and antigen presenting cells, resulted in IL-6 production, which was not observed in similarly cultured CD8+ T cells, indicating a role for T cells.

The cellular source of interleukin-6 during Listeria infection

The cellular source of interleukin-6 (IL-6) during infection of mice with Listeria monocytogenes was investigated both in vitro and in vivo. Peritoneal cells taken at intervals from infected mice and cultured in vitro without added stimulus produced high titers of IL-6 peaking 2 days postinfection in a time course similar to that observed in vivo. Adherent cells with the morphology of macrophages were a major source of this IL-6. Spleen cells similarly harvested at intervals and cultured with heat-killed Listeria or heat-killed Brucella organisms as specific and nonspecific stimuli, respectively, showed two distinct IL-6 responses: (i) an early-phase response up to 5 days after infection when IL-6 production was elicited by either a specific or nonspecific stimulus, and when depletion of T cells had no effect, and (ii) a later response 7 to 10 days after infection when very high levels of IL-6 were produced in response to a specific stimulus. This response was lost when T cells were depleted in vitro or in vivo or in spleen cell cultures from mice with severe combined immunodeficiency. However, studies in vivo failed to show an important role for T cells governing serum IL-6. We conclude that most of IL-6 detected in vivo is produced by nonlymphocytes. Whether IL-6 produced by T lymphocytes in local foci of infection has any role in resolution of that infection is unknown.

Recombinant interleukin-6 protects mice against experimental bacterial infection

Because of reports of high levels of interleukin-6 (IL-6) in patients during infection, we studied the role of IL-6 in experimental infection. Mice infected with the facultative intracellular pathogen Listeria monocytogenes displayed high levels of IL-6 in their sera and tissues, particularly the spleen, 1 to 3 days after infection. At this time, the IL-6 titers correlated with bacterial numbers in individual mice and in groups of mice given graded doses of Listeria organisms. However, the presence of IL-6 in serum declined after 4 days, even when a large initial dose of bacteria meant that bacterial numbers were still increasing at this time. Recombinant mouse IL-6 injected intraperitoneally before infection protected mice in a dose-dependent manner. It was effective when given 4 h before infection but not when administration was delayed for 24 h postinfection. It is therefore believed that IL-6 plays a role in early priming of the immune response to infection. Its exact function in this model is being investigated.

Murine hypersensitivity pneumonitis: bidirectional role of interferon-gamma

C57BL/6 mice were instilled intranasally with optimal doses [150 micrograms of antigen 3 days a week) of the actinomycete Faeni rectivirgula to induce an experimental hypersensitivity pneumonitis. Some control mice received normal rat IgG as controls, whereas other mice received 1 mg weekly of rat anti-murine interferon gamma (IFN-gamma) antibody by the intraperitoneal route and 200 micrograms by the intranasal route given 2 days before and during the challenge period before each instillation. Control mice developed a clear hypersensitivity pneumonitis characterized by an early neutrophilic response at 3 days and a later influx of mononuclear cells (nine- to tenfold increase in cell number. P less than 0.001 vs saline instilled mice at 4 weeks post-treatment). F. rectivirgula instillation determined a sharp increase in the lung index (80% increase in lung weight, P less than 0.005 vs saline treated mice), as well as a significant fibrosis at 4 weeks (twofold increase in lung hydroxyproline levels). Cytokine measurements showed that tumour necrosis factor alpha (TNF alpha) was present in the broncho-alveolar lavage (BAL) of challenged mice at 4 weeks when the BAL was obtained 8 hr after the last challenge (130 U/ml). Treatment of mice with the monoclonal antibody against IFN-gamma was associated with very few changes in the number of cells in the BAL of challenged mice. The lung index of challenged mice was significantly reduced by infusion of the anti-IFN-gamma antibody. Anti-IFN-gamma treatment resulted in decreased levels of TNF alpha in the BAL of F. rectivirgula after 4 weeks of treatment (56 U/ml, P less than 0.01). Moreover, depletion of endogenous IFN-gamma in F. rectivirgula-instilled mice resulted in a diminished lung fibrotic response (P less than 0.01 vs mice treated with F. rectivirgula and control antibody). We also studied the effect of exogenous IFN-gamma adminstration on the development of lung disease. Groups of mice received recombinant gamma interferon (IFN-gamma) (1000 U) intraperitoneally just before the first treatment and also daily, whereas controls received saline or IFN-gamma alone (no F. rectivirgula challenge). After 4 weeks of treatment, mice were killed and various markers of the disease were evaluated. As mentioned before, bronchoalveolar lavage (BAL) cell number was increased tenfold in mice treated with F. rectivirgula, whereas mice given F. rectivirgula and IFN-gamma had only a threefold increase in BAL cell number, determined mostly by a decrease in alveolar macrophage recruitment in the lungs.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhanced resistance against Listeria monocytogenes achieved by pretreatment with granulocyte colony-stimulating factor

Phagocytosis, H2O2 production, Mac-1 expression, and in vivo elimination of Listeria monocytogenes were enhanced in granulocyte colony-stimulating factor (G-CSF)-treated mice. Transfer of polymorphonuclear leukocytes prolonged survival of mice infected with a lethal dose of L. monocytogenes. G-CSF augments the functions of polymorphonuclear leukocytes and thus plays a role in protection.

Effects of macrophage colony-stimulating factor on reduction of viable bacteria and survival of mice during Listeria monocytogenes infection: characteristics of monocyte subpopulations

Mice could well tolerate infection with a lethal dose of Listeria monocytogenes after intraperitoneal preinjections with 250 micrograms of macrophage colony-stimulating factor (M-CSF) per kg of body weight for 5 days. The characteristic changes in the surface markers (Mac-1, LFA-1, and F4/80) of peripheral monocytes were also investigated in order to analyze the mechanism of protection by M-CSF. This investigation shows the excellent effect of intraperitoneal preinjections of M-CSF on the reduction of viable Listeria organisms and the improvement of survival after an intravenous Listeria infection.

Serum cytokine levels in patients with oral mucous membrane disorders

Serum cytokine levels were examined in 18 oral squamous cell carcinoma (SCC), 26 lichen planus (OLP), 20 recurrent aphthous stomatitis (RAS), 8 herpetic gingivostomatitis (HGS), 16 pseudomembrane candidiasis (PMC) and 19 acute bacterial infection (ABI) cases. All SCC and most PMC patients possessed clear serum IL-3. No clear increase of IL-4 was observed in most cases though over 20 pg/ml were found in a few OLP, RAS and ABI. ABI exhibited the highest IL-6, and the cytokine level was lower in RAS, PMC, HGS and OLP in this order. Suppressed IL-6 activity was elevated with improvement of HGS lesion. TNF-alpha increased in 9 OLP, but the levels were below 100 pg/ml in all cases. Most SCC possessed higher GM-CSF activity than the controls. Increase of the cytokine corresponding with improvement of the oral lesion was seen in HGS, but not in OLP. From these results, each serum cytokine seems to reflect a characteristic pathophysiology of individual oral disorder.

Distinction between 'inflammatory' and 'immune' macrophages killing Listeria monocytogenes in murine infection

Two populations of efficiently phagocytic and bacteriolytic cells have been defined in the peritoneal cavity following infection of mice with Listeria monocytogenes. One was the result of a transient inflammatory response 2 days after intraperitoneal (i.p.) infection. It consisted of a mixture of monocyte/macrophages and neurotrophils which, when separated on Percoll gradients or by adherence, were both highly bacteriolytic compared with normal resident peritoneal macrophages. It was rich in recently divided cells as evidenced by in vivo labelling with tritiated thymidine. Although having the enlarged, vacuolated appearance of 'activated' macrophages, three-quarters of the monocyte/macrophages stained positive for myeloperoxidase (MPO), characteristic of monocytes rather than mature macrophages. In contrast, intravenous (i.v.) infection, which localizes in spleen and liver, did not produce this early response in the peritoneal cavity. However, 8 days after either i.v. or i.p. infection there existed in the peritoneal cavity a highly active population of cells comprising chiefly macrophages of typical foamy appearance which did not stain for MPO+. They were actively phagocytic and bacteriolytic and, like the early inflammatory exudate, produced increased amounts of oxygen degradative products. They appear to typify the concept of macrophages activated by T cell mediated immunity. Two day peritoneal exudates induced in these previously infected mice by i.p. rechallenge with L. monocytogenes organisms comprised mostly MPO- macrophages.

The effects of interleukin 3 (IL-3) on cells responsive to macrophage colony-stimulating factor (CSF-1) in liquid murine bone marrow culture

We have examined variation between inbred mouse strains in the proliferative response of bone marrow cells in liquid culture to macrophage colony-stimulating factor (CSF-1) and interleukin 3 (IL-3). In all mouse strains, thymidine incorporation was stimulated by CSF-1 and, after an initial lag period, it reached a peak on day 5. In contrast, two mouse strains, A/J and Balb c, had much lower proliferative responses to IL-3 than did the other strains. In A/J there was no increase in thymidine incorporation above the initial baseline, although the fall in incorporation seen in the absence of any added growth factor was prevented. IL-3 also prevented the loss of CSF-1 responsiveness observed when A/J bone marrow cells were incubated in medium alone. The lag phase in the response to CSF-1 was progressively abolished following IL-3 pre-treatment. Thus, the data with A/J mice separate two distinct activities of IL-3 and show that proliferation is not required for the synergistic effect exerted by IL-3 on CSF-1-stimulated macrophage generation from bone marrow. In strains in which IL-3 alone was able to stimulate proliferation, its action was not additive with that of CSF-1, and addition of both factors together did not overcome the lag phase. This suggests that the two factors act on the same cell population, and that the known synergistic effect of IL-3 on macrophage colony formation in soft agar does not result from an increase in the initial rate of proliferation. The possibility that the combination of factors might alter the duration of the growth response in vivo is discussed.

Treatment of mice with human recombinant interleukin-2 augments resistance to the facultative intracellular pathogen Listeria monocytogenes

The effects of exogenously administered human recombinant IL-2 (hrIL-2) on resistance to Listeria monocytogenes infection were examined. Intravenous injection of hrIL-2 significantly enhanced antibacterial resistance in both BDF1 and C3H/HeJ mice. The beneficial effect of hrIL-2 was observed with as little as 0.6 micrograms per mouse, whereas optimum protection occurred at 6 micrograms per mouse, hrIL-2 was equally protective when administered concomitant with the listeriae or up to 24 h prior to infection; it had little effect if given after the bacterial challenge. Kinetic experiments indicated that both the peak bacterial burden and the time lag before L. monocytogenes began to be cleared from the spleen and liver were reduced in hrIL-2-treated mice as compared with control mice. Histopathological examination of spleens and livers confirmed that hrIL-2-treated Listeria-infected mice experienced considerably less damage to these organs than did control mice. Spleen cells from Listeria-infected mice exhibited depressed levels of mitogen-induced proliferation coincident with the peak bacterial burden in the spleen and liver and during the subsequent recovery from the infection. Administration of hrIL-2 to uninfected mice had no effect on spleen cell proliferation in response to mitogens in vitro, nor did hrIL-2 treatment restore normal levels of splenocyte proliferative responses to Listeria-infected mice. In addition, hrIL-2 treatment resulted in attenuated levels of serum colony-stimulating activity in infected mice as compared with control infected mice. Coadministration of both hrIL-2 and human recombinant interleukin-1 alpha at various dose and time combinations had no detectable additive or synergistic effect. Although these data do not suggest an obvious mechanism of action, they clearly demonstrate that hrIL-2 can augment host defense against the facultative intracellular pathogen L. monocytogenes.

Stimulation of macrophage phagocytic but not bactericidal activity by colony-stimulating factor 1

The ability of mouse peritoneal cells to phagocytose and lyse Listeria monocytogenes was measured after the cells were incubated with purified murine macrophage-specific colony-stimulating factor (CSF-1). Activation of combined phagocytic and bacteriolytic ability required 24 h, with an optimal dose of 1,000 U of CSF-1 per ml. No activation was achieved with a shorter period of incubation, known to be sufficient for GM-CSF to stimulate phagocytosis by granulocytes, and there was no advantage in longer exposure. After 24 h in 1,000 U of CSF-1, macrophages showed visibly increased spreading on the plastic petri dish. Activated cells examined microscopically showed an increase in the number of phagocytic cells and in the numbers of bacteria per phagocytic cell. This increased phagocytic ability was evident also in the increase in the amount of radioactivity associated with the cells following a 30-min incubation with radiolabeled bacteria. When these cells were carefully washed, the percentage of this initial uptake released during the next 2 h was not increased by pretreatment of the cells with CSF-1, showing that the effect of this growth factor was on phagocytosis of the bacteria not on the killing mechanisms per se.

Separate and combined effects of recombinant interleukin-1 alpha and gamma interferon on antibacterial resistance

Our laboratory has previously reported that administration of murine recombinant interleukin 1 alpha (rIL-1 alpha) substantially enhanced the resistance of mice to Listeria monocytogenes infection. Other investigators have reported that gamma interferon (IFN-gamma) plays a pivotal role in antilisteria resistance. In the present study, we have defined doses of human rIL-1 alpha that enhanced the antilisteria resistance of mice. We then addressed the possibility that combined immunotherapy with rIL-1 alpha and recombinant IFN-gamma (rIFN-gamma) might result in an additive or synergistic enhancement of antibacterial resistance. Simultaneous administration of rIL-1 alpha and rIFN-gamma enhanced antilisteria resistance (at 3 days after infection) to a greater extent than did either cytokine alone, although the results did not imply a synergistic action between the two cytokines. Experiments which examined the effects of the timing of cytokine administration indicated that maximal protection was observed when rIL-1 alpha and rIFN-gamma were administered together concomitantly with the L. monocytogenes challenge. When we compared the separate and combined protective effects of rIL-1 alpha and rIFN-gamma throughout the course of a primary L. monocytogenes infection, we observed an additive effect of the two cytokines only at 3 days after challenge, the time at which the peak bacterial burden occurs in the spleens and livers of infected mice. Histopathological comparisons of livers and spleens from cytokine-treated and control listeria-infected mice verified that cytokine treatment reduced the severity of tissue damage in cytokine-treated listeria-infected mice. In an attempt to provide a potential mechanism for the protective effects of rIL-1 alpha and rIFN-gamma administration, we compared levels of colony-stimulating activity in sera from cytokine-treated and control listeria-infected mice. The highest levels of colony-stimulating activity were detected in sera from control listeria-infected mice; somewhat lower levels were found in sera from listeria-infected mice that received rIL-1 alpha and rIFN-gamma either alone or in combination.

Contribution of cytokines to time-dependent augmentation of resistance against Listeria monocytogenes after administration of a traditional Chinese medicine, xiao-chai-hu-tang (Japanese name: shosaiko-to)

The augmentation of resistance against Listeria monocytogenes after an intraperitoneal (ip) administration of shosaiko-to in mice was shown to depend on the time interval between the treatment and the infection. A maximal effect was expressed in mice treated 4 days before ip infection. The time dependent resistance correlated to the accumulation of macrophages in the peritoneal cavity just before the infection, but not to bactericidal activity as judged by the fact that peritoneal macrophages from untreated mice and those from mice treated with shosaiko-to 4 days before showed a high bactericidal activity of the same degree. Resistance to the infection in untreated mice may be attributable to newly accumulating macrophages with a low level of bactericidal activity, but not to resident macrophages with a high level of the activity. After intravenous infection, on the other hand, a maximal effect was expressed in mice treated with shosaiko-to 2 days before. The resistance correlated to accumulation of macrophages and bactericidal activity in the spleen just before the infection. Participation of cytokines in an augmenting effect of shosaiko-to on protection against the infection was examined. Shosaiko-to induced a transient elevation of serum CSF activity that was maximal at 3 hours after the administration in uninfected mice, though it did not augment the CSF activity induced by the infection. The elevation of CSF activity may induce accumulation of macrophages with a high level of bactericidal activity in the spleen 2 days after administration of shosaiko-to and then in the peritoneal cavity 4 days after administration. IFN-gamma and TNF-alpha did not participate in the effect because administration of anti-IFN-gamma or anti-TNF-alpha just before administration of shosaiko-to or just before infection did not abrogate the inhibitory effect of shosaiko-to on the bacterial growth in the early stage of infection. Shosaiko-to also induced an increase of CFUm number in the spleen. The effect may contribute to the augmentation of resistance in the late stage of infection by differentiating to mature macrophages.

Administration of purified anti-L3T4 monoclonal antibody impairs the resistance of mice to Listeria monocytogenes infection

Anti-L3T4 monoclonal antibody (GK1.5) treatment significantly impaired the antilisteria resistance of mice as manifested by increased recovery of listeriae from the spleens and livers of anti-L3T4-treated mice and by greater severity of damage to the liver and other organs. Anti-L3T4-treated mice demonstrated a profound decrease in their T cell-mediated responses to Listeria monocytogenes and its products; they failed to develop delayed type hypersensitivity to soluble listeria antigens in vivo, and their spleen cells proliferated poorly in response to stimulation by either mitogens or listeria antigens in vitro. Spleen cells from control listeria-infected mice produced significant amounts of gamma interferon when stimulated with listeria antigens in vitro, whereas under the same conditions spleen cells from anti-L3T4-treated listeria-infected mice failed to produce detectable gamma interferon. Anti-L3T4 treatment resulted in a slight increase in serum colony-stimulating activity as compared with control listeria-infected mice, probably as a result of the increased bacterial burden in these animals. Despite the dramatic decrease in T-cell activities, anti-L3T4-treated mice succeeded in clearing L. monocytogenes from the spleen and liver in a manner that was only slightly delayed as compared with control listeria-infected mice. In addition, anti-L3T4-treated listeria-immunized mice exhibited a moderate degree of enhanced resistance to rechallenge with L. monocytogenes, and their spleen cells were able to transfer a limited degree of antilisteria resistance to naive recipient mice. Both of these responses, however, were diminished as compared with those of control listeria-immunized mice in the same experiments. Although these observations establish a critical role for L3T4+ cells in the development of maximal resistance to listeriosis, they also suggest that compensatory mechanisms may allow mice to develop considerable antilisteria resistance even when L3T4+ cell activities are substantially reduced.

Response of the murine hematopoietic system to chronic infection with Mycobacterium lepraemurium

Mycobacterium lepraemurium infection of mice produces a chronic lethal disease that is characterized by massive accumulation of macrophages throughout the mononuclear-phagocyte system. We studied the influence of M. lepraemurium infection on the composition and function of the hematopoietic system. Medullary erythropoiesis was virtually abolished, as reflected by a small number of erythroid elements and a decrease in the number and frequency of erythroid progenitors in the bone marrow, together with reduced uptake of 59Fe into bone marrow hemin. On the other hand, erythropoiesis was observed in the spleen, as demonstrated by a large number of erythroid cells, a sixfold increase of 59Fe uptake, and a pronounced increase in the number of erythroid progenitors. A considerable increase of monocyte progenitors was observed in the spleen, and a more modest increase was observed in the bone marrow. This increase may be accounted for, at least in part, by greatly increased levels of macrophage-colony-stimulating factor in the serum of infected mice. Thus, M. lepraemurium infection produces important changes in the hematopoietic system, during the course of which the spleen becomes the major hematopoietic organ.

Macrophage production during murine listeriosis: colony-stimulating factor 1 (CSF-1) and CSF-1-binding cells in genetically resistant and susceptible mice

The concentration of the macrophage-specific colony-stimulating factor (CSF-1) and the numbers of bone marrow and spleen cells with specific receptors for that factor have been investigated in a number of mouse strains under normal conditions and after infection with the facultative intracellular bacterium Listeria monocytogenes. The CSF-1 concentration in serum and tissue was markedly elevated in infected mice, the degree of stimulation reflecting the dose of L. monocytogenes. The CSF-1 titer did not correlate with genetic resistance or susceptibility of the mice to L. monocytogenes. In contrast to the effect of lipopolysaccharide, Listeria infection was able to increase the level of CSF-1 in the lipopolysaccharide nonresponder strain C3H/HeJ. In line with earlier findings on colony-forming cells, cells bearing receptors for CSF-1 in uninfected susceptible BALB/cJ mice were only half those in resistant C57BL/6J mice. After infection the majority of these cells disappeared from the bone marrow and spleen cells of both resistant and susceptible mice. The number of CSF-1 receptor-bearing cells in the normal bone marrow may determine the degree of resistance to L. monocytogenes.

Assay for quantitation of mature monocytes in murine haemopoietic tissues

We propose a new assay which allows the extent of production of mature monocytes in murine haemopoietic tissues to be monitored with precision. To develop such a quantitative assay, we chose a T-cell function easily detectable in vivo, namely the ability of T lymphocytes to locally transfer a delayed-type hypersensitivity (DTH) reaction. T cells co-transferred with antigen into footpads of syngeneic mice are mediators of DTH through their ability to recruit phagocytes recently produced in haemopoietic tissues. Therefore, if recipients of DTH-mediating T cells (DTH-T cells) are depleted of phagocytes by lethal irradiation given 36 to 48 h before local transfer of these DTH-T cells mixed with antigen, they no longer respond by a DTH reaction, measured as an increase in footpad thickness, unless they receive i.v. bone marrow cells as a source of recruitable phagocytes. In such conditions, the footpad thickness increase is linearly related to the number of cells injected i.v. Pretreatment of bone marrow cells with the rat IgG2b F4/80 monoclonal antibody abolishes their ability to restore expression of DTH, indicating that monocytes (F4/80+ cells) are the phagocytes to be measured. This assay system thus provides a means of measuring levels of recruitable mature monocytes present in haemopoietic tissues. One illustration of the assay is given by the study of the recovery of recruitable phagocytes in bone marrow following a single treatment with cyclophosphamide.

Production of colony-stimulating factors (CSFs) during infection: separate determinations of macrophage-, granulocyte-, granulocyte-macrophage-, and multi-CSFs

After infection of mice with Listeria monocytogenes, elevated levels of colony-stimulating factors (CSFs) in the serum were quantitated by six different assays: ability to stimulate colony formation, the proliferation of 2 suspension of bone marrow cells (both measuring total colony-stimulating activity), a radioimmunoassay for macrophage-CSF (CSF-1), the WEHI-3B differentiation assay for granulocyte-CSF, and proliferation of 32D-c1-3 and FDC-P1 cell lines (specific for multi-CSF and either multi- or granulocyte-macrophage-CSFs, respectively). The great bulk of serum colony-stimulating activity represented macrophage- and granulocyte-CSFs, with small but measurable amounts of granulocyte-macrophage-CSF. The degree of elevation of serum CSF depended on the infecting dose used and the numbers of bacteria growing in the spleens and livers of the two mouse strains compared, i.e., L. monocytogenes-resistant C57BL/10 and susceptible BALB/cJ. The increase in serum CSFs occurred before the peak in bone marrow granulocyte-macrophage progenitors and before the reduction in bacterial numbers which follows the onset of specific cell-mediated immunity.

Serum colony stimulating activity and colony forming cells in murine brucellosis: relationship to immunopathology

Intravenous injection of mice with Brucella abortus vaccine strain 19, results in a chronic infection, immunity to which is dependent on T cell activation of the macrophages. A major feature of the infection is splenomegaly characterized by massive numbers of macrophages. We report here investigations of the haemopoietic precursors of macrophages, the colony forming cells (CFC), and the growth factors, colony stimulating factors (CSF), controlling their production. Comparison was made amongst three mouse strains, CBA, BALB/c and C57B1/10, as well as the F1 (CBA x BALB/c), which differ in the degree of splenomegaly developed and their ability to rid themselves of infection. The proportion of colony forming cells in the spleen peaked 2 to 3 weeks after infection and was higher in those strains which developed stronger splenomegaly. On the other hand there was no relation between colony forming cells and ability to control infection. Serum CSF also peaked 2-3 weeks post infection, with similar titres in all mouse strains studied. Bone marrow exhibited an early loss of total cellularity after infection followed by recovery. There was a sharp peak in the proportion of colony forming cells in the bone marrow 2 weeks post infection. Spleen and bone marrow CFC and serum CSF all returned to normal levels before infection was resolved.

Recombinant murine interleukin-1 alpha enhancement of nonspecific antibacterial resistance

In this study we report that treatment with recombinant murine interleukin-1 alpha (rIL-1 alpha) significantly enhanced the resistance of mice to infection by the facultative intracellular pathogen Listeria monocytogenes. The greatest level of protection was observed at a dose of 1,000 lymphocyte-activating factor units (approximately 0.17 micrograms) of rIL-1 alpha per mouse. Although rIL-1 alpha enhanced antibacterial resistance when administered either intravenously or intraperitoneally, greater protection was observed when the rIL-1 alpha and the L. monocytogenes challenge were given by the same parenteral route. When the intravenous route was used, antibacterial resistance was maximal when the rIL-1 alpha and L. monocytogenes were injected concomitantly. In contrast, intraperitoneal administration of rIL-1 alpha was most effective when given 48 h before an intraperitoneal L. monocytogenes challenge. Based on the following lines of evidence, we concluded that contaminating lipopolysaccharide (LPS) was unlikely to be responsible for the enhanced antibacterial resistance that was observed: (i) LPS was not detectable (less than 0.2 ng/ml by the lysate assay) at the concentration of rIL-1 alpha that was injected; (ii) polymyxin B did not abrogate rIL-1 alpha-enhanced antibacterial resistance; (iii) rIL-1 alpha treatment enhanced the antibacterial resistance of LPS-nonresponsive C3H/HeJ mice; and (iv) injection of up to 10 micrograms of LPS per mouse (calculated to be greater than 50,000 times the concentration of LPS in the rIL-1 alpha administered) failed to duplicate the marked enhancement of antibacterial resistance that was mediated by rIL-1 alpha. These data provide evidence for the beneficial role of IL-1 in nonspecific antibacterial resistance.

Effect of acute nutritional deprivation on macrophage colony-stimulating factor and macrophage progenitor cells in mice

The effect of short-term nutritional deprivation on host defenses and on the parameters of macrophage production was determined in outbred mice. Confirming previous data from this laboratory, initial experiments demonstrated that starved mice were relatively resistant to infection by Listeria monocytogenes as determined by spleen and liver bacterial counts. The number of macrophage progenitor cells in bone marrow rose slightly during a 72-h starvation period and returned to normal during refeeding. By contrast, the number of progenitor cells in spleens fell to 12% of the base line during starvation. The concentration of the macrophage colony-stimulating factor in serum decreased during starvation and returned to normal during refeeding. Additional experiments were performed to determine whether starved mice had increased parameters of macrophage production during listerial infection. The number of progenitor cells in the bone marrow and spleens of starved mice had increased compared with that of fed mice early in infection. Macrophage colony-stimulating factor levels in starved mice rose early and remained elevated during infection but were not as high as in fed mice. These data document the changes in the parameters of monocyte production during starvation and suggest that the number of macrophage progenitor cells may be related to increased resistance to L. monocytogenes.

The in vitro bactericidal activity of peritoneal and spleen cells from Listeria-resistant and -susceptible mouse strains

Two days after Listeria-resistant (LrR) C57BL/10 mice were infected intraperitoneally with Listeria, their peritoneal macrophages demonstrated enhanced bactericidal activity beyond that seen in susceptible (LrS) BALB/c or CBA mice. Intravenous infection had no effect on peritoneal cell activity. The induction, but not expression, of the enhanced activity was radiosensitive. There was no significant difference between the strains with respect to the number of cells or cellular composition of the exudates. No difference in the in vitro chemotactic response of cells from the two strains could be demonstrated. Therefore there seems to be recruitment to the infected peritoneal cavity of C57BL/10 mice of young, efficiently bactericidal monocytes/macrophages. On the other hand, spleen cell bactericidal activity was intrinsically superior in C57BL/10 mice compared with BALB/c mice, possibly because, as a haemopoietic organ, the C57BL/10 spleen already contains high numbers of these efficient monocytes.