Fluorescent fusion proteins have revolutionized examination of proteins in living cells. Still, studies using these proteins are met with criticism because proteins are modified and ectopically expressed, in contrast to immunofluorescence studies. However, introducing immunoreagents inside cells can cause protein extraction or relocalization, not reflecting the in vivo situation. Here we discuss pitfalls of immunofluorescence labeling that often receive little attention and argue that immunostaining experiments in dead, permeabilized cells should be complemented with live-cell imaging when scrutinizing protein localization.

Immunolabeling artifacts and the need for live-cell imaging

Stress and surgery have been suggested to compromise host resistance to infectious and malignant diseases in experimental and clinical settings. Because stress affects numerous physiological systems, the role of the immune system in mediating such effects is unclear. In the current study, we assessed the degree to which stress-induced alterations in natural killer (NK) cell activity underlie increased susceptibility to tumor development in F344 rats. Two stress paradigms were used: forced swim and abdominal surgery. Host resistance to tumor development was studied using 3 tumor models syngeneic to inbred F344 rats: CRNK-16 leukemia and the MADB106 mammary adenocarcinoma, both sensitive to NK activity, and the NK-insensitive C4047 colon cancer. Swim stress increased CRNK-16-associated mortality and metastatic development of MADB106 but not metastasis of C4047 cells. In both stress paradigms, stress suppressed NK activity (NKA) for a duration that paralleled its metastasis-enhancing effects on the MADB106 tumor. In vivo depletion of large granular lymphocyte/NK cells abolished the metastasis-enhancing effects of swim stress but not of surgical stress. Our findings indicate that stress-induced suppression of NKA is sufficient to cause enhanced tumor development. Under certain stressful conditions, suppression of NKA is the primary mediator of the tumor-enhancing effects of stress, while under other conditions, additional factors play a significant role. Clinical circumstances in which surgical stress may induce enhanced metastatic growth are discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291097-0215%2819990315%2980%3A6%3C880%3A%3AAID-IJC14%3E3.0.CO%3B2-Y

Evidence that stress and surgical interventions promote tumor development by suppressing natural killer cell activity.

Hypoxia-ischemia induces an inflammatory response in the immature central nervous system that may be important for development of brain injury. Recent data implicate that chemoattractant cytokines, chemokines, are involved in the recruitment of immune cells. The aim was to study α- and β-chemokines in relation to the temporal activation of inflammatory cells after hypoxia-ischemia in immature rats. Hypoxia-ischemia was induced in 7-day-old rats (left carotid artery occlusion + 7.7% oxygen). The pups were decapitated at different times after the insult. Immunohistochemistry was used for evaluation of the inflammatory cell response and RT-PCR to analyze the cytokine mRNA and chemokine mRNA expression. A distinct interleukin-1β and tumor necrosis factor-α cytokine expression was found 0-24 h after hypoxia-ischemia that was accompanied by induction of α-chemokines (growth related gene and macrophage inflammatory protein-2). In the next phase, the β2-integrin expression was increased (12 h and onward) and neutrophils transiently invaded the vessels and tissue in the infarct region. The mRNA induction for the β-chemokines macrophage inflammatory protein-1α, macrophage inflammatory protein-1β, and RANTES preceded the expression of markers for lymphocytes [cluster of differentiation (CD)4, CD8], microglia/macrophages (MHC I), and natural killer cells in the infarct area. The activation of microglia/macrophages, CD4 lymphocytes, and astroglia persisted up to at least 42 d of postnatal age implicating a chronic component of immunoinflammatory activation. The expression of mRNA for α- and β-chemokines preceded the appearance of immune cells suggesting that these molecules may have a role in the inflammatory response to insults in the immature central nervous system.

/pdf/chemokine-and-inflammatory-cell-response-to-hypoxia-ischemia-2pqkjsalqf.pdf

Chemokine and inflammatory cell response to hypoxia-ischemia in immature rats.

Aging is associated with lymphopenia and progressive decline in T cell functions; however, the mechanisms underlying these defects are unclear. We analyzed the expression of genes promoting apoptosis (fas/fasL1 and bax) and those inhibiting apoptosis (bcl-2 and bcl-xL) in lymphocytes from aging and young subjects at the protein level, using flow cytometry/Western blotting, and at the mRNA level, using quantitative PCR. Susceptibility of T cell subsets to undergo anti-Fas-induced apoptosis was analyzed by propidium iodide staining, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) assay, DNA fragmentation assay, and staining with Hoechst 33342 dye. An increased expression of Fas and Fas ligand and a decreased expression of Bcl-2 were observed in both CD4+ and CD8+ T cells from aging as compared with young controls. Increased Fas and decreased Bcl-2 expression were also found in memory cells of both CD4+ and CD8+ T cell subsets from aging. Bax expression was increased in lymphocytes from aging at both the protein and mRNA level. No significant difference was observed in Bcl-xL expression between aging and young; however, the ratio of Bax:Bcl-xL was increased in aging. An increased proportion of CD4+ and CD8+ T cell subsets from aging underwent apoptosis following anti-Fas Ab treatment as compared with CD4+ and CD8+ T cell subsets from young controls. These data suggest that increased apoptosis may be one of the mechanisms responsible for lymphopenia and T cell deficiency associated with human aging.

Increased Apoptosis of T Cell Subsets in Aging Humans: Altered Expression of Fas (CD95), Fas Ligand, Bcl-2, and Bax

Although acute stress has been reported to suppress natural killer cell activity (NKA) and host resistance to metastasis, it is unclear whether the sympathetic nervous system (SNS) has a role in these

Suppression of NK Cell Activity and of Resistance to Metastasis by Stress: A Role for Adrenal Catecholamines and β-Adrenoceptors

A cell fixation and permeabilization procedure consisting of sequential paraformaldehyde and methanol was evaluated and found suitable for concomitant flow cytometric quantification of total cellular DNA, immunofluorescence measurements of cell surface proteins, and immunofluorescence measurements of intracellular proteins. Paraformaldehyde/methanol-fixed cells exhibited significantly greater intracellular antitubulin immunofluorescence than cells fixed with paraformaldehyde or methanol alone (p less than 0.002) and significantly greater intracellular antitubulin immunofluorescence than cells fixed with methanol followed by paraformaldehyde (p less than 0.006). With paraformaldehyde/methanol fixation, cell morphology was well preserved and forward and right angle light scatter properties were sufficiently well maintained to permit gating on these parameters. Cell surface marker staining with fluorescent anti-leukocyte antibodies was unaffected by fixation with paraformaldehyde/methanol. Paraformaldehyde effects on the intensity of DNA staining with propidium iodide were dependent on paraformaldehyde concentration and fixation temperature; these effects were least pronounced at low paraformaldehyde concentrations (0.25% or less), and at temperatures lower than 37 degrees C. Paraformaldehyde fixation may result in differences in propidium iodide staining of DNA in some diploid cells, which may produce small spurious aneuploid peaks in normal peripheral blood leukocytes. Paraformaldehyde fixation also produces an apparent increase in the DNA index of aneuploid cell populations in comparison with methanol fixation, particularly when the DNA index exceeds 1.5. Occasionally, this paraformaldehyde fixation-induced effect is useful in identifying biologically distinct near-diploid subpopulations in tumors.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cyto.990130414

Sequential paraformaldehyde and methanol fixation for simultaneous flow cytometric analysis of DNA, cell surface proteins, and intracellular proteins.

Flow cytometric cell sorting is commonly used to obtain purified subpopulations of cells for use in in vitro and in vivo assays. This can be time-consuming if the subpopulations of interest represent very low percentages of the cell suspension under study. Often the desired subpopulations are identified by two-color immunofluorescence staining. Generally, cell sorting is performed with a flow cytometer configured to trigger on light scatter signals, then sort windows are set based upon the signals from both fluorescent markers. We demonstrate that triggering the cytometer with the fluorescence signal from antibody staining common to both of the desired subpopulations, then sorting the subpopulations based upon staining of a second marker, substantially increases the speed of cell sorting vis-a-vis traditional methods. This is because undesired events are not analysed, allowing an increase in the throughput rate. While desired subpopulations of cells can be obtained by this method, undesired (i.e., nonstaining) cell "contaminants" increase and may require a second sort. The combined time for the initial enrichment sort and a second sort can be less than sorting once using standard methodology. Alternatively, the degree of contamination may be controlled by adjusting the concentration of the cell suspension and by the sample flow rate.

Sorting minor subpopulations of cells: use of fluorescence as the triggering signal.

In this report, we present data on heterogeneity of rat NK cells utilizing a combination of antibody and lectin-binding characteristics. Among NKR-P1bright NK cells, two discrete populations characterized as Lycopersicon esculentum lectin (L.E.)bright (60 to 80%) and L.E.dim (20 to 40%) were identified by flow cytometry. Comparison of the morphology of sorted NKR-P1bright/L.E.bright and NKR-P1bright/L.E.dim cells indicated that both were greater than 90% LGL. An analysis of the functional capabilities of the sub-populations indicated that NKR-P1bright/L.E.bright NK cells were more efficient in lysis of YAC-1 target cells (1743 LU20/10(7) cells) than were NKR-P1bright/L.E.dim cells (504 LU20/10(7) cells). Conversely, NKR-P1bright/L.E.dim NK cells were much more efficient at lysis of antibody-sensitized erythrocytes (antibody-dependent cellular cytotoxicity (ADCC)) (1412 LU20/10(7) cells) than were NKR-P1bright/L.E.bright cells (165 LU20/10(7) cells). Lysis of antibody sensitized P815 target cells yielded similar results as NKR-P1bright/L.E.dim cells and NKR-P1bright/L.E.bright cells had 905 LU20/10(7) and 189 LU20/10(7), respectively. Additional experiments indicated that NKR-P1bright/L.E.bright NK cells had the capacity to trigger lytic activity via NKR-P1 whereas NKR-P1bright/L.E.dim NK cells did not. NKR-P1bright/L.E.bright sorted cells had a greater capacity to form conjugates with YAC-1 target cells than did NKR-P1bright/L.E.dim sorted cells. Conversely, NKR-P1bright/L.E.dim NK cells were demonstrated to form E-A rosettes whereas the NKR-P1bright/L.E.bright NK cells were not. Additional experiments indicated that tomato lectin itself was not responsible for the differences in reverse ADCC activity or ADCC activity among the subsets. However, lysis of YAC-1 target cells was modulated to some degree by the lectin. These data indicate that NKR-P1bright/L.E.bright and NKR-P1bright/L.E.dim subpopulations of rat NK cells have different capacities for: 1) triggering through NKR-P1; and 2) E-A rosette formation and lysis of antibody-sensitized target cells by ADCC.

Functional heterogeneity between NKR-P1bright/Lycopersicon esculentum lectin (L.E.)bright and NKR-P1bright/L.E.dim subpopulations of rat natural killer cells.

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Sequential paraformaldehyde and methanol fixation for simultaneous flow cytometric analysis of DNA, cell surface proteins, and intracellular proteins.

Sorting minor subpopulations of cells: use of fluorescence as the triggering signal.

Functional heterogeneity between NKR-P1bright/Lycopersicon esculentum lectin (L.E.)bright and NKR-P1bright/L.E.dim subpopulations of rat natural killer cells.