M. F. Geertsma

Decreased Expression of ζ Molecules by T Lymphocytes Is Correlated with Disease Progression in Human Immunodeficiency Virus—Infected Persons

In human immunodeficiency virus type 1 (HIV-1) infection, functional activities of T lymphocytes are impaired. Analogous to tumor-infiltrating T lymphocytes from cancer patients, in whom poor proliferative responses are associated with fewer zeta molecules, this study compared expression of CD3zeta molecules by T lymphocytes from HIV-infected persons and healthy controls. Flow cytometry and immunoblotting revealed significantly diminished zeta expression by CD3, CD4, and CD8 T lymphocytes from AIDS patients but not from persons without AIDS. zeta-mRNA levels were also decreased in cells from AIDS patients. CD3zeta expression correlated significantly with CD4 cell counts and HIV-1 RNA levels; impaired expression of CD3zeta molecules appeared to be reversible upon virus load reduction following highly active antiretroviral treatment (HAART). Thus, reduced expression of CD3zeta molecules by T lymphocytes from HIV-infected persons correlates with disease status. Investigations into CD3zeta expression by subpopulations of peripheral T lymphocytes and by T lymphocytes in lymphoid tissues will contribute to the understanding of immune reconstitution of HIV-infected patients following HAART.

Arachidonic acid, but not its metabolites, is essential for FcγR-stimulated intracellular killing of Staphylococcus aureus by human monocytes

Since arachidonic acid (AA) production by phospholipase A2 (PLA2) is essential for the Fcγ receptor (FcγR)‐mediated respiratory burst and phagocytosis of opsonized erythrocytes by monocytes and macrophages, we focused in this study on the role of AA and its metabolites in the FcγR‐stimulated intracellular killing of Staphylococcus aureus by human monocytes. The results revealed that the PLA2 inhibitors, but not inhibitors of cyclo‐oxygenase and lipoxygenase, markedly suppressed the FcγR‐mediated killing process. The production of O−2 by monocytes upon FcγR cross‐linking was inhibited by 4‐bromophenacyl bromide in a dose‐dependent fashion, indicating that inhibition of PLA2 activity impairs the oxygen‐dependent bactericidal mechanisms of monocytes, which could be partially restored by addition of exogenous AA and docosahexaenoic acid, but not myristic acid. These polyunsaturated fatty acids, but not myristic acid, stimulated the intracellular killing of S. aureus by monocytes, although not as effectively as FcγR cross‐linking. Furthermore, FcγR cross‐linking stimulated the release of AA from monocytes. Studies with selective inhibitors revealed that the FcγR‐mediated activation of PLA2 is dependent on Ca2+ and tyrosine kinase activity. Together these results indicate a key role for PLA2/AA, but not its major metabolites, in mediating the FcγR‐stimulated intracellular killing of S. aureus by monocytes.

Monocytes incubated with surfactant: a model for human alveolar macrophages?

Monocytes migrate to the lungs and enter the alveoli where they come into contact with surfactant and differentiate into alveolar macrophages. This study focused on the question of the extent to which monocytes and monocyte‐derived macrophages (MDM) incubated with surfactant resemble alveolar macrophages. Surfactant‐incubated monocytes shared with alveolar macrophages the intracellular presence of surfactant, efficient phagocytosis of opsonized Staphylococcus aureus, and poor intracellular killing of ingested bacteria. The suppressive effect of surfactant on bactericidal activities of monocytes could not be attributed to either the surfactant lipid fraction or surfactant protein A. Monocytes incubated with surfactant differed from alveolar macrophages with respect to expression of various Fc and complement receptors involved in intracellular killing of bacteria. Surfactant‐incubated monocytes produced significantly more H2O2 upon stimulation with phorbol ester than alveolar macrophages, but significantly less than control monocytes. Together, monocytes and MDM incubated with surfactant, although similar to alveolar macrophages in some aspects, are not an adequate model for alveolar macrophages. Most likely, factors other than surfactant in the microenvironment of the alveoli, such as oxygen tension, play a role in the differentiation of monocytes to alveolar macrophages as well. J. Leukoc. Biol. 62: 485–492; 1997.

Different effect of granulocyte colony-stimulating factor or bacterial infection on bone-marrow cells of cyclophosphamide-treated or irradiated mice.

In the present study, the effect of treatment with granulocyte colony‐stimulating factor (G‐CSF) on cellular composition of the bone marrow and the number of circulating leucocytes of granulocytopenic mice, whether or not infected with Staphylococcus aureus, was assessed. With two monoclonal antibodies, six morphologically distinct cell populations in the bone marrow could be characterised and quantitated by two‐dimensional flow cytometry. Granulocytopenia was induced by cyclophosphamide or sublethal irradiation. Cyclophosphamide predominantly affected the later stages of dividing cells in the bone marrow resulting in a decrease in number of granulocytic cells, monocytic cells, lymphoid cells and myeloid blasts. G‐CSF administration to cyclophosphamide‐treated mice increased the number of early blasts, myeloid blasts and granulocytic cells in the bone marrow, which indicates that this growth factor stimulates the proliferation of these cells in the bone marrow. During infection in cyclophosphamide‐treated mice the number of myeloid blasts increased. However, when an infection was induced in cyclophosphamide and G‐CSF‐treated mice, the proliferation of bone‐marrow cells was not changed compared to that in noninfected similarly treated mice. Sublethal irradiation affected all bone‐marrow cell populations, including the early blasts. G‐CSF‐treatment of irradiated mice increased only the number of myeloid blasts slightly, whereas an infection in irradiated mice, whether or not treated with G‐CSF, did not affect the number of bone‐marrow cells. Together, these studies demonstrated that irradiation affects the early blasts and myeloid blasts in the bone marrow more severely than treatment with cyclophosphamide. Irradiation probably depletes the bone marrow from G‐CSF‐responsive cells, while cyclophosphamide spared G‐CSF responsive cells, thus enabling the enhanced G‐CSF‐mediated recovery after cyclophosphamide treatment. Only in these mice, bone marrow recovery is followed by a strong mobilisation of mature granulocytes and their band forms from the bone marrow into the circulation during a bacterial infection.

Interleukin-10 Has Different Effects on Proliferation of Listeria monocytogenes in Livers and Spleens of Mice

ABSTRACT The aim of this study was to investigate the effect of interleukin-10 (IL-10) on the course of Listeria monocytogenes infection in naive and immune mice. Treatment with IL-10 during the course of a primary infection significantly decreased the number of bacteria in the spleen and did not affect the number in the liver. During a secondary infection in immune mice treated with IL-10, the number of bacteria was significantly lower in the spleen but significantly higher in the liver in comparison to mock-treated immune mice. IL-10 treatment during a primary Listeria infection decreased the concentration of gamma interferon (IFN-γ) in plasma and the toxoplasmastatic activity of macrophages, whereas it increased the percentage of mildly CD3-positive T cells in the spleen. During a secondary infection, the concentration of IFN-γ in plasma was decreased on day 1 but remained unaffected during later days of infection. From these results, we conclude that IL-10 has different effects on the proliferation of L. monocytogenes in the spleen and liver during primary and secondary Listeriainfections.

Ingestion of pulmonary surfactant by human monocytes inhibits their antibacterial functions

Alveolar macrophages are believed to play a critical role in the maintenance of the integrity of the lungs by both ingesting potentially harmful agents, such as allergens and infectious microorganisms, and producing a number of specific mediators, such as reactive oxygen intermediates, arachidonic acid metabolites, chemotactic factors, and cytokines (1). These macrophages reside in a microenvironment which is rich in surfactant and they also contain this material (2, 3). Surfactant, comprising about 90% lipid, 8% protein, and 2% carbohydrates, is produced by type 2 epithelial alveolar cells; its main function is to reduce surface tension in the alveoli (4). Despite their strategic position outside the epithelial lining of the air spaces, alveolar macrophages are limited in their bactericidal activities compared to other phagocytes (5–7).

Activation of Phagocytes by Recombinant Interferon-γ

Lymphokines are formed by CD4+ lymphocytes in response to an antigen. During the course of an infectiTn with human immune deficiency virus (HIV) the number of CD4+ lymphocytes decreases. In patients with AIDS this number is so low that the immunoregulatory functions of lymphokines, e.g. the activation of phagocytes and of endothelial cells, fails and a condition of cellular immunodefiency occurs. Interferon-γ (IFN-γ) is considered to be the main lymphokine involved in activating phagocytes. However, the effect of IFN-γ on the bactericidal activities of phagocytes is not well established. Since pure murine and human recombinant IFN-γ (rIFN-γ) in relative large quantities became available, in vitro and in vivo studies and experimental therapies could be performed. The present contribution summarizes our and other studies on the activation of murine macrophages and human granulocytes by rIFN-γ.