Mitogen-induced T-cell CD69 expression is a less sensitive measure of T-cell function than [(3)H]-thymidine uptake

CD69 expression as an index of T-cell function: assay standardization, validation and use in monitoring immune recovery

BACKGROUND

CD69 is a surrogate marker of T-cell responsiveness to mitogen and Ag stimulus and can be used as a measure of T-lymphocyte activation. Quantitative flow cytometric determination of CD69 expression on T lymphocytes has several advantages over traditional lymphocyte proliferation assays, but this method has not yet been standardized for clinical applications.

METHODS

We qualified a commercially available assay using the manufacturer's procedures for measurement of T-cell response to a mitogen (PHA), superantigen (Staphylococcus endotoxin B; SEB) and Ca(2+) ionophore (phorbyl myristate acetate; PMA) with peripheral blood from healthy volunteers. Following this, we tested the usefulness of the assay in determining T-cell responses to PHA and SEB for six immunocompromised patients.

RESULTS

Healthy volunteers showed 17-fold increases in T-cell CD69 Ab bound per cell (ABC) with PHA stimulation compared with the baseline. SEB was also an effective T-cell activating agent, increasing CD69 ABC by 5-fold, comparable with results obtained with PMA stimulation. PHA- and SEB-stimulated T-cell CD69 ABC for patients 100 days post-BM transplant were generally below 1 SD of that from healthy volunteers. SEB-stimulated T-cell CD69 expression was significantly depressed for CD8(+) T cells while CD4(+) T-cell responses to SEB were generally within 1 SD of the mean for healthy volunteers.

DISCUSSION

These results suggest that quantitative measurement of CD69 surface expression by flow cytometry is a useful diagnostic tool for detailed assessment of T-lymphocyte and subset activation.

Markers to measure immunomodulation in human nutrition intervention studies

Normal functioning of the immune system is crucial to the health of man, and diet is one of the major exogenous factors modulating individual immunocompetence. Recently, nutrition research has focused on the role of foods or specific food components in enhancing immune system responsiveness to challenges and thereby improving health and reducing disease risks. Assessing diet-induced changes of immune function, however, requires a thorough methodological approach targeting a large spectrum of immune system parameters. Currently, no single marker is available to predict the outcome of a dietary intervention on the resistance to infection or to other immune system-related diseases. The present review summarises the immune function assays commonly used as markers in human intervention studies and evaluates their biological relevance (e.g. known correlation with clinically relevant endpoints), sensitivity (e.g. within- and between-subject variation), and practical feasibility. Based on these criteria markers were classified into three categories with high, medium or low suitability. Vaccine-specific serum antibody production, delayed-type hypersensitivity response, vaccine-specific or total secretory IgA in saliva and the response to attenuated pathogens, were classified as markers with high suitability. Markers with medium suitability include natural killer cell cytotoxicity, oxidative burst of phagocytes, lymphocyte proliferation and the cytokine pattern produced by activated immune cells. Since no single marker allows conclusions to be drawn about the modulation of the whole immune system, except for the clinical outcome of infection itself, combining markers with high and medium suitability is currently the best approach to measure immunomodulation in human nutrition intervention studies. It would be valuable to include several immune markers in addition to clinical outcome in future clinical trials in this area, as there is too little evidence that correlates markers with global health improvement.

Assessing immune function changes in exercise and diet intervention studies

PURPOSE OF REVIEW

To discuss the advantages and limitations of the methods currently available to assess changes in human immune function in response to interventions such as changes in diet or exercise.

RECENT FINDINGS

Much recent research has focused on the effect of regular moderate exercise and the role of foods or specific food components in enhancing immune system responsiveness to challenge and thereby improving health and reducing disease risk. The present review summarizes the issues in experimental design that need to be considered in human intervention studies, the immune function variables commonly used as markers in such studies and the biological relevance (e.g. known correlation with clinically relevant endpoints) of the markers. In-vivo markers appear to be the best. Markers of peripheral blood leukocyte function are also of value since they may provide information on the mechanism(s) of change caused by an intervention.

SUMMARY

Currently, no single marker of human immune function is available to predict the outcome of an exercise or dietary intervention on the resistance to infection or to other immune system-related diseases. There is too little evidence at present that correlates individual markers with global health improvement and therefore assessing changes of immune function requires a thorough methodological approach targeting a large spectrum of parameters.

Comparative analysis of lymphocyte activation marker expression and cytokine secretion profile in stimulated human peripheral blood mononuclear cell cultures: an in vitro model to monitor cellular immune function

Activation of lymphocytes is a complex, yet finely regulated cascade of events that results in the expression of cytokine receptors, production and secretion of cytokines and expression of several cell surface molecules that eventually lead to divergent immune responses. Assessing the qualitative and quantitative nature of lymphocyte function following immunotherapy provides valuable information about the immune responses mediated by a therapeutic agent. To facilitate evaluation of the immunomodulatory activity of therapeutic agents, we have established a platform of in vitro immunoassays with normal human peripheral blood mononuclear cells (PBMCs) treated with several polyclonal activators that are known to exhibit different modes of action. We evaluated the kinetics of cell surface marker expression and cytokine release from PBMCs stimulated in parallel with various activating agents over a time course. These stimulating agents induced early (CD69 and CD71) and late (CD25 and HLA-DR) activation markers to varying antigen densities, indicated different cytokine profiles, and showed differential inhibition with dexamethasone (DEX), an inhibitor of early signaling events. Based on the association or correlation of the kinetics of activation marker expression and secreted cytokines, the results of our study indicate the appropriate time points for the simultaneous measurement of both these activation products. This study defines the kinetics for both measures of T cell activation and provides a comprehensive review with various polyclonal activators that can serve as a reference for monitoring lymphocyte function in clinical study samples.

Cofilin peptide homologs interfere with immunological synapse formation and T cell activation

The formation of supramolecular activation clusters within the immunological synapse, crucial for sustained signaling and T lymphocyte activation, requires costimulation-dependent reorganization of the actin cytoskeleton. Here we have identified the actin-remodeling protein cofilin as a key player in this process. Cell-permeable peptides that block costimulation-induced cofilin/F-actin interactions in untransformed human T lymphocytes impair receptor capping and immunological synapse formation at the interface between T cells and antigen-presenting cells. As a consequence, T cell activation, as measured by cytokine production and proliferation, is inhibited.

Exercise-induced changes to in vitro T-lymphocyte mitogen responses using CFSE

Carboxyfluorescein diacetate succinamidyl ester (CFSE) labeling of lymphocyte populations can provide unique insights into cell function at rest and with exercise, due to its ability to quantify cell division on an individual cell basis. This study aimed to characterize the effect of acute, intense exercise on T-lymphocyte function. Well-trained endurance runners completed 60 min of treadmill running at 95% of individual anaerobic threshold. Blood samples were collected before exercise; after 30 and 60 min of exercise; and after 30, 60, and 90 min of recovery. Isolated peripheral blood mononuclear cells were labeled with CFSE and cultured with or without mitogen (phytohemagglutinin). After culture, cell suspensions were labeled with CD3 (allophycocyanin) and CD8 (phycoerythrin), and expansion rates and cell death rates were calculated for each sample, as well as mitosis rates for each cell generation. Exercise was associated with a 60% decrease in cell expansion in both CD4 and CD8 cell types from before exercise to midexercise (P < 0.05). The significant decrease in expansion rate in the midexercise samples for both cell types was mirrored by a 65% increase in cell death (P < 0.05) in both cell types at that sample point. Exercise had no effect on the mitosis rate of either CD4 or CD8 cells in any cell generation (generations 0-3). This study indicates that 1 h of intense exercise affects in vitro T-lymphocyte function. These data suggest, for the first time, that exercise decreases cell expansion rate via an increase in cell death of both CD4 and CD8 T lymphocytes, rather than a decrease in mitosis.