Spontaneous aggregation as a mechanism for human monocyte purification

A previously unreported property of human mononuclear phagocytes is the ability of these cells to spontaneously aggregate. Fresh mononuclear cells obtained after plateletpheresis were noted to spontaneously form large cellular aggregates. Dual parameter immunofluorescence analysis demonstrated that the aggregating cells were positive for the monocyte marker CD11 (complement receptor, type 3) but were negative for the lymphocyte marker CD3 (T3 antigen). In addition, less than 5% of the nonaggregating cells were CD11+, suggesting that almost all CD11+ cells aggregated. Cellular aggregates were independent of cell concentration and formed more efficiently at 4 degrees C than at either 22 or 37 degrees C. Based on these observations, a purification procedure utilizing Ficoll-Hypaque separation, spontaneous aggregation at 4 degrees C, and transient plastic adherence resulted in a sevenfold enrichment of the CD11+ peripheral blood monocytes. Purified monocytes were contaminated with less than 2% CD3 cells. The size, growth, and adherence characteristics as well as cytologic stains indicated that the monocytes were not significantly altered by the purification procedure. Thus, spontaneous aggregation is an efficient and convenient method for the isolation of large numbers of purified monocytes.     

Induction of allogeneic cytolytic T lymphocytes by partially purified membrane glycoproteins

It has been previously shown that P815 (H-2^d) purified plasma membranes can induce cytolytic activity from primed C57BL/6 (H-2^b) spleen cells. The secondary cytolytic T lymphocyte (CTL) inducing activity is retained when these P815 plasma membranes are solubilized in deoxycholate. Evidence is now presented that the cell surface antigens responsible for CTL induction can be partially purified in active form and these antigens can be incorporated into reconstituted membranes and phospholipid vesicles. The active antigens have the properties expected for H-2 molecules on lentil lectin chromatography and gel filtration.     

Requirements for modulation of the CD4 molecule in response to phorbol myristate acetate. Role of the cytoplasmic domain

CD4 (T4) is a 60 kD glycoprotein expressed on a subset of T lymphocytes. CD4 augments T cell responses to suboptimal Ag stimulation. In addition, the CD4 molecule is the receptor for HIV-1. CD4 is phosphorylated on serine residues within the cytoplasmic domain and its cell surface expression is decreased in response to PMA, APC bearing the appropriate Ag or HIV infection. The kinetics of CD4 phosphorylation and modulation are similar, suggesting that the two events may be related. L3T4, the murine CD4 equivalent, is not modulated from the surface of mature, peripheral T cells in response to PMA. The difference in the ability to modulate L3T4 and CD4 in response to PMA may be due to differences between the two molecules or to differences between the cells in which they are expressed. To further define the requirements for CD4 modulation, we used retroviral vectors to transfer the cDNA for CD4 and various mutants of CD4 into two murine T cell hybridomas that express L3T4. One of these hybridomas, By155.16, does not modulate L3T4 in response to PMA and the other, 5D5.63, does modulate L3T4 in response to PMA. When expressed by these hybridomas CD4 is not modulated from the surface of By155.16 and is modulated from the surface of 5D5.63 in response to PMA. In both of these hybridomas, CD4 is phosphorylated on serine residues in response to PMA. A mutant form of CD4, CD4 delta, was constructed in which the majority of the cytoplasmic domain was deleted. When expressed in 5D5.63, CD4 delta was not modulated in response to PMA. Replacing the cytoplasmic domain of CD4 with that of the human IL-2 receptor did not reconstitute the ability of CD4 to be modulated. These results suggest that the inability to modulate L3T4 from the surface of murine peripheral T cells is due to features of the cell and not the molecule. Furthermore, the cytoplasmic domain of CD4 is required for its modulation from the cell surface in response to PMA.     

Gene flow in environmental Legionella pneumophila leads to genetic and pathogenic heterogeneity within a Legionnaires’ disease outbreak

Background

Legionnaires’ disease is a severe form of pneumonia caused by the environmental bacterium Legionella pneumophila. Outbreaks commonly affect people with known risk factors, but the genetic and pathogenic complexity of L. pneumophila within an outbreak is not well understood. Here, we investigate the etiology of the major Legionnaires’ disease outbreak that occurred in Edinburgh, UK, in 2012, by examining the evolutionary history, genome content, and virulence of L. pneumophila clinical isolates.

Results

Our high resolution genomic approach reveals that the outbreak was caused by multiple genetic subtypes of L. pneumophila, the majority of which had diversified from a single progenitor through mutation, recombination, and horizontal gene transfer within an environmental reservoir prior to release. In addition, we discover that some patients were infected with multiple L. pneumophila subtypes, a finding which can affect the certainty of source attribution. Importantly, variation in the complement of type IV secretion systems encoded by different genetic subtypes correlates with virulence in a Galleria mellonella model of infection, revealing variation in pathogenic potential among the outbreak source population of L. pneumophila.

Conclusions

Taken together, our study indicates previously cryptic levels of pathogen heterogeneity within a Legionnaires’ disease outbreak, a discovery that impacts on source attribution for future outbreak investigations. Furthermore, our data suggest that in addition to host immune status, pathogen diversity may be an important influence on the clinical outcome of individual outbreak infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0504-1) contains supplementary material, which is available to authorized users.     

Interferon-gamma induction of LFA-1-mediated homotypic adhesion of human monocytes

Cell-cell adhesion plays an important role in monocyte function. To investigate the molecular basis for monocyte adhesion, we used recombinant interferon-gamma to induce the formation of homotypic monocyte adhesions. The induction of homotypic adhesions correlated with the increased expression of the LFA-1 membrane molecule. LFA-1 surface expression was increased twofold, whereas expression levels of other monocyte surface molecules including CR3 and p150,95 were unchanged. The direct involvement of LFA-1 in monocyte adhesion was addressed by anti-LFA-1 monoclonal antibody inhibition of homotypic adhesions. Two monoclonal antibodies to distinct epitopes on the LFA-1 alpha-chain completely inhibited homotypic adhesions. Antibodies to a variety of other monocyte surface molecules, often present at higher cell surface density than LFA-1, did not inhibit homotypic adhesion. A panel of monoclonal antibodies that recognized different functional epitopes on the LFA-1 alpha-chain inhibited homotypic monocyte in a hierarchy identical to that observed in previous studies of cell-mediated cytotoxicity. These findings suggest that LFA-1 serves an adhesive function for human mononuclear phagocytes. In addition to providing a molecular basis for homotypic monocyte adhesions, the results suggest a more general role for LFA-1 in monocyte adhesion reactions.     

Interleukin-3 (IL-3)-induced c-fos activation is modulated by Gab2-calcineurin interaction

Interleukin-3 (IL-3) regulates cell growth by affecting various processes such as cell death, survival, and proliferation. Cues from the external environment are sensed by surface receptors, and complex signaling mechanisms arise within the cells, leading to specific functional outcomes. In this study, we demonstrate that the cytokine IL-3 induces the activation of the Ca(2+)-dependent phosphatase, calcineurin (Cn). Furthermore Cn dephosphorylates Gab2, resulting in c-fos activation and cell proliferation. We also report that there is a direct interaction between Cn and Gab2 upon IL-3 stimulation, and Akt can regulate this interaction.     

Uncoupling p70(s6) kinase activation and proliferation: rapamycin-resistant proliferation of human CD8(+) T lymphocytes

Rapamycin is a fungal macrolide that inhibits the proliferation of T cells. Studies in both animals and humans have found that rapamycin significantly reduces graft rejection. However, though CD8(+) T cells are involved in graft infiltration and rejection, little is known regarding the effects of rapamycin on CD8(+) human T cell responses. In this study, we examined the mechanism of rapamycin-induced inhibition of Ag-driven activation of CD8(+) T cells. Surprisingly, a heterogeneous proliferative response in the presence of rapamycin was observed among different Ag-specific CD8(+) T cell clones; this was also observed in CD8(+) peripheral blood T cells activated with TCR cross-linking ex vivo. Inhibition of T cell proliferation by rapamycin was controlled by both the strength of signal delivered through the Ag receptor as well as the specific costimulatory signals received by the T cell. Rapamycin-resistant proliferation occurred despite inhibition of p70(s6) kinase activity. Moreover, rapamycin-resistant proliferation of the CD8(+) T cell clones was blocked by anti-IL-2 Abs, suggesting that while some of the parallel pathways triggered by IL-2R signaling are sensitive to the effects of rapamycin, others account for the Ag-driven rapamycin resistance. These data provide a new framework for examining the specific mechanism of action of rapamycin in human disease.