Cytokine flow cytometry: Assessing cytokine production at the single cell level

Autologous nucleus pulposus primes T cells to develop into interleukin-4-producing effector cells: an experimental study on the autoimmune properties of nucleus pulposus

An autoimmune response to herniated nucleus pulposus has been proposed to constitute a pathophysiologic mechanism for inducing sciatica based on the fact that nucleus pulposus under normal conditions is excluded from the development of immunological tolerance. The manifestation of an autoimmune response comprises different steps starting with antigen capture, continuing with activation of T helper (T(H)) cells and ending with production of autoantibodies. Activated T(H) cells differentiate into either T(H)1 cells, predominately producing proinflammatory cytokines such as interferon gamma (IFNgamma) or a T(H)2 subset mainly producing anti-inflammatory cytokines such as interleukin-4 (IL-4). The aim of the present study was to examine if exposure of autologous nucleus pulposus (NP) to the immune system for 3 weeks is potent enough to prime T(H) cells to differentiate into T(H)2 cells. The study was performed in a pig model allowing the exposure of NP to the immune system. To assess the polarization of T(H) cells the intracellular production of IFNgamma and IL-4 was measured in T cells by using flow cytometry. The revealed predominant production of IL-4 together with low production of IFNgamma in T cells after NP exposure to the immune system indicates that nucleus pulposus may prime T(H) cells to develop into IL-4-producing T(H)2 cells after being exposed to the immune system, for example, in association with disc herniation.

Longitudinal study of intracellular T cell cytokine production in infants compared to adults

Intracellular cytokine production in lymphocytes obtained longitudinally from 325 healthy infants aged 2-12 months was compared with adult lymphocytes using four-colour flow cytometry. Peripheral blood samples (180 microlitres) were stimulated with phorbol 12-myristate 13-acetate, ionomycin and brefeldin A to induce production and intracellular accumulation of cytokines. The method was validated by assessing reproducibility, repeatibility, ruggedness (i.e. fresh versus day-old blood samples), precision, linearity and sensitivity. Among infants, the number and percentage of T lymphocytes (helper/inducer T cell subsets and cytotoxic/suppressor T cell subsets) producing IFN-gamma (type 1) and IL4 (type 2) increased over the first year of life but remained significantly lower than levels found in adults. In both infants and adults more CD4- T cells than CD4+ T cells were induced to make IFN-gamma. Infant Th1/Th2 ratios revealed modest Th1-skewed (predominant) profiles compared to adults, which were 5-10 times higher. Infant Tc1/Tc2 ratios revealed Tc1-skewed responses which were equal to adult ratios by age 12 months. At 12 months infant Th2 responses were closer to adult levels than were Th1 cells. Intracellular cytokine detection by flow cytometry is a rapid, sensitive, rugged and precise method to characterize immune status changes over time.

Detection of intracellular tumor necrosis factor alpha in stimulated fetal cells

BACKGROUND

It is unknown if immature fetal cells produce tumor necrosis factor (TNF) alpha in the same manner that adult cells do. The aim of this study was to determine the feasibility of early detection of intracellular TNF produced by circulating human monocytes (Mo) and lymphocytes (Ly) using flow cytometry and to compare the stimulation profiles of mature and fetal cells.

MATERIAL AND METHODS

Fetal umbilical cord blood (n = 10) and adult volunteer blood (n = 10) were obtained. In vitro stimulation with endotoxin (LPS) and ionomycin-PMA was performed. Brefeldin A was added to prevent extracellular transport of TNF. Cell type was determined by using CD-14 marker separating monocyte and lymphocyte populations. Anti-human TNF monoclonal antibody was used to detect intracellular TNF by flow cytometry analysis.

RESULTS

Thirty to sixty thousand cells were analyzed per sample. Average TNF expression of stimulated fetal Mo was 28.2%, and that of fetal Ly was only 1.1%. Adult stimulated Ly had an average TNF expression of 31.9%, and adult Mo, 29.6% (P < 0.05 for adult Ly vs fetal Ly).

CONCLUSION

TNF flow cytometry analysis allows assessment of individual cell types and their ability to produce that cytokine. Fetal cells are able to produce TNF when stimulated, but the stimulation profile of Ly differs from that of adult samples. This observation may be of clinical importance in evaluating the response of immature cells to a septic stimulus. Flow cytometry is reliable, reproducible, quick, and easily obtained from a small sample of peripheral blood. Clinical use will be applicable once appropriate controls are developed, as reported in this study.

Rapid assessment of antigen induced cytokine expression in memory T cells by flow cytometry

Methods for analysis of T cell responses to specific antigen have traditionally relied on measurements of proliferation or cytokine expression in bulk cultures of PBMC in long term incubations with putative antigen. These techniques suffer from the drawback that they do not enable analysis of single cell responses in the context of unselected cellular backgrounds. It is increasingly important to not only identify cells on the basis of expression of unique surface antigens but also to determine functional and molecular parameters of individual cells in response to a variety of stimuli. We have recently developed methodologies to rapidly assess T-cell subset responses to polyclonal activators and specific antigen in whole blood. These procedures determine the percentages of activated cells and the identification of leucocyte subsets capable of expressing various cytokines and cell surface antigens. Multiparameter analysis of CD69+ /cytokine + expression in T cells in response to specific antigen (e.g. CMV, mumps) demonstrated a range of frequencies from 0.05% to 5.0% within 6 h. Frequencies of responding T cells were consistent but varied depending upon the antigen. Antigen specific T cell responses were host specific and both positively and negatively regulated by antibodies to co-receptors involved in APC-T cell interactions. These technologies will be discussed in terms of application to problems of measuring immune function parameters in disease. The modified technique described in this report is compatible with simple and rapid analysis of clinical samples and provides a means to directly examine the effects of in vivo drug concentrations on T cell immunity. Studies are in progress to examine the sensitivity of this cellular assay to drugs and other therapeutic modalities in clinical samples.

Detection of antigen-specific T cell cytokine expression in whole blood by flow cytometry

We have recently described a highly sensitive flow cytometric technique, based on the ability to detect single cell expression of cytokines, to simultaneously quantitate and phenotypically characterize antigen-specific memory/effector T cells in PBMC cultures. In this report, we describe a simplified procedural modification which enables the rapid detection of low frequency memory CD4+ and CD8+ T cells expressing cytokines in response to soluble antigen in whole blood. When compared with T cell responses in PBMC cultures, whole blood cultures demonstrated similar but slightly higher percentages of T cells responsive to specific antigen. In addition, T cell responses to cytomegalovirus in whole blood were observed only in sensitized (seropositive) individuals, and CD4+ T cell responses could be blocked by anti-class II MHC antibodies. This procedure may provide a means to examine direct effects of pharmacological drug concentrations on T cell immunity in clinical samples.

Simultaneous detection of DNA synthesis and cytokine production in staphylococcal enterotoxin B activated CD4+ T lymphocytes by flow cytometry

Assessment of T cell activation has traditionally been performed by measuring proliferation as a function of 3[H]-thymidine incorporation, or secretion of cytokines from activated peripheral blood mononuclear cells (PBMC) in culture. An alternative method for detection of proliferation at the single cell level utilizes incorporation of bromodeoxyuridine (BrdU), an analog of thymidine, into cellular DNA. After appropriate fixation and permeabilization of the cells, a monoclonal antibody (mAb) against BrdU conjugated with a fluorescent dye is employed to measure by flow cytometry the incorporated BrdU. Here, we report a flow cytometric procedure which can be used for the simultaneous detection of BrdU incorporation, activation markers such as CD69 and CD25, and intracellular cytokines in T cell subsets from activated PBMC. Our observations are consistent with the proposal that cytokine synthesis and cell proliferation occur sequentially in CD4+ T cells stimulated with the superantigen staphylococcal enterotoxin B (SEB). The majority of cells expressing the cytokines IFN-gamma and IL-2 at 48 h appear to have undergone DNA synthesis, however all proliferating cells do not express IFN-gamma or IL-2. The methods presented in this report offer a unique approach for studying simultaneous expression of key cellular activation events in phenotypically resolved lymphocyte populations.