Cytokine immunoassays: recommendations for standardisation, calibration and validation

Sleep disturbance and activation of cellular and transcriptional mechanisms of inflammation in older adults

BACKGROUND

Sleep disturbance, including poor subjective sleep quality and insomnia disorder, is common in older adults and associated with increases in age-related morbidity risk. Accumulating evidence implicates inflammation as an underlying mechanism. In two complementary studies, we examined whether sleep disturbance is associated with activation of cellular and transcriptional mechanisms of inflammation in older adults.

METHODS

Study 1 examined whether healthy older adults with poor subjective sleep quality (n = 62), compared to those with good subjective sleep quality (n = 101), differed in monocytic production of interleukin (IL)-6 and/or tumor necrosis factor (TNF)-α following stimulation with lipopolysaccharide. Study 2 examined whether older adults with insomnia disorder (n = 17), compared to those without insomnia disorder (n = 25), differed in the regulation of transcription factors (TFs) related to immune activation (i.e., nuclear factor-κB/Rel family), sympathetic nervous system (SNS) activity (i.e., cAMP-response element-binding protein), hypothalamic-pituitary-adrenal (HPA) axis activity (i.e., glucocorticoid receptor) and anti-viral responses (i.e., interferon-regulatory factor/interferon-stimulated response element) assessed in peripheral blood mononuclear cells.

RESULTS

In Study 1, older adults with poor subjective sleep quality, compared to those with good subjective sleep quality, showed higher percentages of stimulated monocytes producing IL-6 only (25.4 ± 16.8 % vs 20.4 ± 13.9 %; p < 0.05, η_p² = 0.03), producing TNF-α only (37.6 ± 13.1 % vs 31.2 ± 14.3 %; p < 0.01, η_p² = 0.05), and co-producing IL-6/TNF-α simultaneously (17.8 ± 11.7 % vs 13.9 ± 9.6 %; p < 0.05, η_p² = 0.03). In Study 2, older adults with insomnia disorder, compared to those without insomnia disorder, showed higher TF activity related to immune activation (p's < 0.05) and SNS function (p's < 0.001), along with lower TF activity related to HPA axis function (p's < 0.05).

CONCLUSION

In older adults, poor subjective sleep quality and insomnia diagnosis are associated with increases in monocytic cytokine production and changes in TF activity related to immune activation, SNS function, and HPA axis function. Activation of markers of cellular and transcriptional inflammation might contribute to the link between sleep disturbance and age-related morbidity risk.

Circulating versus lipopolysaccharide-induced inflammatory markers as correlates of subthreshold depressive symptoms in older adults

Objectives: Circulating cytokines have been associated with depression, but their detection has limitations, which may be overcome by direct detection of intracellular cytokines (ICCs) after lipopolysaccharide (LPS) stimulation in vitro. This study compared circulating versus LPS-induced inflammatory markers as correlates of subthreshold depressive symptoms.Methods: Secondary data analysis of a cross-sectional insomnia study in healthy community-dwelling older adults was conducted. In 117 participants (≥55 years), plasma tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), C-reactive protein (CRP) and in vitro LPS-induced monocyte production of IL-6 and TNF-α were assayed. Depressive symptoms were assessed using the clinician-rated Inventory of Depressive Symptomatology (IDS-C). Multivariate linear regression was conducted to test the associations between inflammatory markers and subthreshold depressive symptoms in the entire sample as well as in subgroups stratified into higher and lower inflammation levels.Results: LPS-induced TNF-α (adjusted β = 0.28, p = .04), IL-6 (0.29, p = .03) and TNF-α + IL-6 (0.43, p = .001) significantly positively correlated with subthreshold depressive symptoms only in higher inflammation subgroups. No circulating biomarkers positively correlated in any subgroups. In the entire sample, no biomarkers were significantly associated with subthreshold depressive symptoms.Conclusions: LPS-induced cytokines may be more sensitive correlates of subthreshold depressive symptoms than circulating cytokines, particularly in older adults with higher systemic inflammation.Clinical Trials Registry: ClinicalTrials.gov NCT00280020.

Lipopolysaccharide-stimulated intracellular cytokines and depressive symptoms in community-dwelling older adults

Background

Inflammation is involved in the pathophysiology of depression, and circulating inflammatory cytokines have been associated with depressive symptoms. However, measuring circulating cytokines have inherent methodological limitations. In vitro lipopolysaccharide (LPS)-stimulated intracellular cytokines (ICCs) overcome these limitations. Furthermore, because psychosocial and physiological stressors activate inflammatory responses and LPS-stimulated ICCs reflect the inflammatory responsivity of monocytes to such stressors, ICCs may reflect individual stress responsivity.

Methods

This cross-sectional study examined whether LPS-stimulated expression of ICCs in peripheral blood mononuclear cells (PBMCs) is a sensitive inflammation measure correlated with depressive symptoms in 180 community-dwelling older adults. We tested correlations of not only intracellular but also circulating inflammatory markers with depressive symptoms assessed using the 10-item Center for Epidemiological Studies Depression Scale (CES-D). Intracellular markers included expression of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and both in PBMCs. Circulating markers included IL-6, TNF-α, and C-reactive protein (CRP) in plasma.

Results

None of the correlations were statistically significant. However, in contrast to circulating markers, the correlations of ICCs were consistently in the expected direction, i.e., higher ICC expression correlating with higher depression severity.

Discussion

Despite the non-significant findings, further research is required for the evaluation of LPS-stimulated ICC expression as biomarkers of depressive symptoms.

Comparison of 2 Sample Processing Methods and 9 Commercial Immunoassays for the Detection of Interleukin-1α in the Serum of Patients with Abdominal Aortic Aneurysm

BACKGROUND

For a cytokine to have a role as a clinically useful biomarker, it must be measureable in a practical, reliable, and reproducible manner. Furthermore, assays from different manufacturers should produce comparable results. The aim of this paper was to examine the effect of 2 sample processing methodologies and compare 9 commercially available immunoassays for their measurement of serum interleukin (IL)-1α in patients with abdominal aortic aneurysm.

METHODS

Two sample processing methodologies and 9 manufacturers' immunoassays were compared. Each immunoassay was also tested for detection of both IL-1α isoforms.

RESULTS

A positive signal for IL-1α was found in all serum samples, in all immunoassays, using both processing methods. In the majority, titer concentrations were unquantifiable with values below manufacturers' detectable range. Variability in titer concentrations was seen across all immunoassays. With the exception of 1 immunoassay, all were able to detect both IL-1α isoforms.

CONCLUSIONS

Researchers wishing to measure serum cytokines levels should be aware that differences in sample processing methods and manufacturers' immunoassays can affect the results. This may result in misleading conclusions being drawn about biological processes underpinning a wide range of inflammatory diseases.

Cytokine responses to exercise and activity in patients with chronic fatigue syndrome: case-control study

Chronic fatigue syndrome (CFS) is characterized by fatigue after exertion. A systematic review suggested that transforming growth factor (TGF)-β concentrations are often elevated in cases of CFS when compared to healthy controls. This study attempted to replicate this finding and investigate whether post-exertional symptoms were associated with altered cytokine protein concentrations and their RNA in CFS patients. Twenty-four patients fulfilling Centers for Disease Control criteria for CFS, but with no comorbid psychiatric disorders, were recruited from two CFS clinics in London, UK. Twenty-one healthy, sedentary controls were matched by gender, age and other variables. Circulating proteins and RNA were measured for TGF-β, tumour necrosis factor (TNF), interleukin (IL)-8, IL-6 and IL-1β. We measured six further cytokine protein concentrations (IL-2, IL-4, IL-5, IL-10, IL-12p70, and interferon (IFN)-γ). Measures were taken at rest, and before and after both commuting and aerobic exercise. CFS cases had higher TGF-β protein levels compared to controls at rest (median (quartiles) = 43·9 (19·2, 61·8) versus 18·9 (16·1, 30·0) ng/ml) (P = 0·003), and consistently so over a 9-day period. However, this was a spurious finding due to variation between different assay batches. There were no differences between groups in changes to TGF-β protein concentrations after either commuting or exercise. All other cytokine protein and RNA levels were similar between cases and controls. Post-exertional symptoms and perceived effort were not associated with any increased cytokines. We were unable to replicate previously found elevations in circulating cytokine concentrations, suggesting that elevated circulating cytokines are not important in the pathophysiology of CFS.

Adrenergic Effect on Cytokine Release After Ex Vivo Healthy Volunteers' Whole Blood LPS Stimulation

Catecholamines are molecules with immunomodulatory properties in health and disease. Several studies showed the effect of catecholamines when administered to restore hemodynamic stability in septic patients. This study investigates the effect of norepinephrine and dobutamine on whole blood cytokine release after ex vivo lipopolysaccharide (LPS) stimulation. Whole blood collected from healthy individuals was stimulated with LPS, in the presence of norepinephrine or dobutamine at different concentrations, with or without metoprolol, a β1 receptor antagonist. Cytokine measurement was performed in isolated cell culture supernatants with ELISA. Results are expressed as mean ± SEM and compared with Mann-Whitney rank-sum test. Both norepinephrine and dobutamine significantly reduced TNF-α and IL-6 production after ex vivo LPS stimulation of whole blood in a dose-dependent manner, and this effect was partially reversed by the presence of metoprolol. Norepinephrine and dobutamine reduce the LPS-induced production of pro-inflammatory cytokines, thus possibly contributing to altered balance between the inflammatory and anti-inflammatory responses, which are vital for a successful host response to severe disease, shock, and sepsis.

Methodological Issues in Cytokine Measurement in Schizophrenia

There is mounting evidence that inflammation is a major factor in the pathophysiology of schizophrenia. Inflammatory status is commonly ascertained by measuring peripheral cytokine concentrations. An issue concerning research on inflammation and schizophrenia relates to assay methodology. Enzyme-linked immunosorbent assay (ELISA) is the most widely used and the gold standard method used to measure cytokine concentrations. ELISA has a number of limitations. Both ELISA and multiplex are limited by not being able to distinguish between bioactive and inactive molecules and the matrix and heterophilic (auto-) antibody interference. Multiplex assays when combined with gene expression analysis and flow cytometry techniques such as fluorescence-activated cell sorting may be useful to detect abnormalities in specific immune pathways. Peripheral blood mononuclear cells cultures, to evaluate in vitro lipopolysaccharide-induced cytokine production, may be a better technology than measuring cytokines in the serum. The purpose of this paper is to shed light on major methodological issues that need to be addressed in order to advance the study of cytokines in schizophrenia. We make a few recommendations on how to address these issues.

Optimization of buffer solutions to analyze inflammatory cytokines in gingival crevicular fluid by multiplex flow cytometry

Objective: the aim of this study was to test two buffer solutions in order to attain a reliable and reproducible analysis of inflammatory cytokines (IL-1β, IL-6, TNF-α, OPG, OPN and OC), in gingival crevicular fluid (GCF) by flow cytometry. Material and Methods: GCF samples from healthy volunteers were collected with perio-paper strips and diluted either in phosphate buffered saline (PBS) or Tris-HCl buffer, with and without protease inhibitors (PI). Cytokine immunoassays were carried out by flow cytometry (Luminex Xmap 200) generating standard curves. Results: standards curves generated with the use of phosphate-buffered saline (PBS) demonstrated best adjustment for cytokines IL-1ß, IL-6 and TNF- α levels, when using Tris-HCl (p<0.05). Conclusions: The use of PBS buffer with the addition of PI provided reliable measurements of inflammatory biomarkers in GCF samples of healthy volunteers.

Key words:Curve fitting, flow cytometer, immunoassay buffer, crevicular fluid, cytokines.

Cytokines as biomarkers in rheumatoid arthritis

RA is a complex disease that develops as a series of events often referred to as disease continuum. RA would benefit from novel biomarker development for diagnosis where new biomarkers are still needed (even if progresses have been made with the inclusion of ACPA into the ACR/EULAR 2010 diagnostic criteria) and for prognostic notably in at risk of evolution patients with autoantibody-positive arthralgia. Risk biomarkers for rapid evolution or cardiovascular complications are also highly desirable. Monitoring biomarkers would be useful in predicting relapse. Finally, predictive biomarkers for therapy outcome would allow tailoring therapy to the individual. Increasing numbers of cytokines have been involved in RA pathology. Many have the potential as biomarkers in RA especially as their clinical utility is already established in other diseases and could be easily transferable to rheumatology. We will review the current knowledge's relation to cytokine used as biomarker in RA. However, given the complexity and heterogeneous nature of RA, it is unlikely that a single cytokine may provide sufficient discrimination; therefore multiple biomarker signatures may represent more realistic approach for the future of personalised medicine in RA.

Identification of patients with chronic obstructive pulmonary disease (COPD) by measurement of plasma biomarkers

INTRODUCTION

Inflammation is an important constituent of the pathology of chronic obstructive pulmonary disease (COPD), leading to alveolar destruction and airway remodelling.

OBJECTIVE

The aim of this study was to assess the difference in plasma biomarkers of inflammation between asymptomatic smokers and patients with COPD.

METHODS

We used commercially available enzyme-linked immunosorbent assay kits to measure the plasma levels of tumour necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), matrix metalloproteinase-9 (MMP-9), monocyte chemotactic protein-1 (MCP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1) and tissue inhibitor of metalloproteinase-2 (TIMP-2) on two occasions with a 2-week interval in patients with COPD (n = 20), asymptomatic smokers (n = 10) and healthy lifelong non-smokers (n = 10). The participants were characterised clinically, physiologically and by quantitative computed tomography by measuring the relative area of emphysema below -910 Hounsfield units (RA-910).

RESULTS

The results of the biomarker measurements on the two occasions were highly reproducible. Patients with COPD had significantly higher plasma levels of IL-8 (P = 0.004) and significantly lower levels of TIMP-1 (P = 0.02) than smokers and non-smokers. There was no statistically significant difference between the three groups in the level of TNF-alpha, MMP-9, MCP-1 and TIMP-2. The IL-8/TIMP-1 ratio correlated significantly with the degree of airway obstruction measured as forced expiratory volume in 1 second (FEV(1)) % predicted (r = -0.47, P < 0.01); with the diffusion capacity (r = -0.41, P < 0.01); and with the grade of emphysema measured as RA-910 (r = 0.39, P = 0.01).

CONCLUSION

These findings suggest that the measurement of plasma biomarkers, such as IL-8/TIMP-1, may aid to discriminate patients with COPD from smokers at lower risk of developing COPD.

Targeting interferon alpha subtypes in serum: a comparison of analytical approaches to the detection and quantitation of proteins in complex biological matrices

The targeted detection and quantitation of proteins in complex biological fluids such as blood is as analytically challenging as it is crucial for biomedical research. Antibody-based techniques such as the ELISA are the current standards for such measurements, having in favorable cases high specificity and pg/mL detection limits. Long development timelines and susceptibility to cross reactivity have led researchers to investigate mass spectrometric alternatives. The literature contains diverse schemes for sample preparation and multiple platforms for mass spectrometric detection. Critical evaluations of competing technologies are, however, badly needed. Taking closely related subtypes of the pro-inflammatory cytokine interferon alpha as a test case, we compared a sample preparation workflow based on affinity enrichment to one based on generic multidimensional chromatography, and evaluated mass spectrometric techniques using tandem mass spectrometry on low resolution ion traps, high resolution "accurate mass tags," and triple quadrupole selective reaction monitoring. Each workflow and detection method proved capable of detecting and discriminating between these proteins at or below the ng/mL level in human serum. Quantitation by isotope dilution was evaluated using full length protein as the internal standard. Both triple quadrupole selected reaction monitoring and orbitrap selected ion monitoring produced linear calibration curves from 1 ng/mL to 1 microg/mL, with lower limits of quantitation below 5 and 50 ng/mL, respectively.

Multiplexed Analysis of Biomarkers Related to Obesity and the Metabolic Syndrome in Human Plasma, Using the Luminex-100 System

Background: The complex pathology of disease has sparked the development of novel protein expression profiling techniques that require validation in clinical settings. This study focuses on multiplexed analyses of adipocytokines and biomarkers linked to the metabolic syndrome, diabetes, and cardiovascular disease.

Methods: Multiplexed immunoassays using fluorescent microspheres and the Luminex-100 system were performed on plasma from 80 obese patients (40 with the metabolic syndrome) before and after 6–8 weeks of diet-induced weight loss. Leptin, insulin, C-peptide, monocyte chemoattractant protein-1 (MCP-1), eotaxin, interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), and IL-6 concentrations measured with multiplex panels from 3 different manufacturers were compared with results from commercial ELISAs. Detection limits and between- and within-run imprecision were determined for each analyte. Bland–Altman analysis was used to determine agreement between multiplexed immunoassays and ELISAs.

Results: Correlation between the Luminex multiplexed assays and ELISAs was good for leptin (Linco), insulin (Linco), MCP-1 (Biosource and Upstate), and eotaxin (Biosource) with correlation coefficients of 0.711–0.895; fair for eotaxin (Upstate) and C-peptide (Linco) with correlation coefficients of 0.496–0.582; and poor for TNF-α, IL-8, and IL-6 (Linco, Biosource, Upstate, and R&D) with correlation coefficients of −0.107 to 0.318. Within- and between-run imprecision values for the multiplex method were generally &lt;15%. Relative changes in plasma leptin and insulin concentrations after diet-induced weight loss were similar whether assessed by multiplex assay or ELISA.

Conclusion: Although this technology appears useful in clinical research studies, low assay sensitivity and poor correlations with conventional ELISA methods for some analytes with very low plasma concentrations should be considered when using the Luminex platform in clinical studies.

Seasonal variation in whole blood cytokine production after LPS stimulation in normal individuals

We examined seasonal differences in whole blood cytokine production after endotoxin (LPS) stimulation in 17 healthy individuals from an urban area having normal sleep/wakefulness pattern. We used 500 pg/ml of LPS for incubation period of 4 h to stimulate 100 microl of whole blood of the same subjects in June, September, February, and March. We found no differences in the circulating total WBCs and differentials including monocytes between different seasons. We found during September (autumn) a reduced pro-inflammatory cytokine production in terms of TNF-alpha and IL-6 production compared to the other seasons. We also found a reduced anti-inflammatory cytokine production in June (summer) and September (autumn) in terms of IL-10, TNF-RI and TNF-RII compared to February (winter) and March (spring). Our results suggest that in early summer there is a predominating pro-inflammatory cytokine response which is counterbalanced early in autumn. These results may have significant implications in the determination of reference values, in exploration of immune response and inflammatory disease prevalence between different seasons, in determining LPS tolerance (immunoparalysis) and planning clinical trials and immunomodulary therapies. However, the effect of dark/light exposure differences on the circadian periodicity in the responsiveness of immune cells during different seasons should be further investigated.

Strategies for detection, measurement and characterization of unwanted antibodies induced by therapeutic biologicals

An important aspect of evaluating the safety of therapeutic biologicals is the assessment of the unwanted immunogenicity of such biologicals in recipients. Properly planned immunogenicity studies with appropriately devised strategies are critical if valid conclusions concerning the unwanted immunogenicity are to be derived. Such studies need to be conducted using carefully selected and validated procedures. Several techniques are available for detection and measurement of immunogenicity including immunoassays, radioimmunoprecipitation assays (RIPAs), surface plasmon resonance (SPR) and bioassays. A combination of methods for characterization of the induced antibodies is usually necessary for a detailed understanding of the type(s) of antibodies generated against a therapeutic product. This review considers the benefits and limitations of the various techniques available for antibody detection and outlines a strategy for the assessment of unwanted immunogenicity of therapeutic products.

TNFalpha production in whole blood cultures from healthy individuals

Tumor necrosis factor alpha (TNFalpha) is a major mediator of inflammatory responses and also plays a prominent role in bridging the innate and adaptive phases of immunity. In the present work we attempted to study TNFalpha production in endotoxin-stimulated blood of healthy individuals, and the inter-individual variability in TNFalpha production. For this study, we used diluted whole blood stimulated with lipopolysaccharide (LPS). The levels of the pro-inflammatory cytokine TNFalpha were measured by ELISA and by the L929 cytotoxicity bioassay in 16 and 18 healthy donors, respectively. There were highly significant inter-individual variations in the induced TNFalpha production. It is worth noting that there was no difference in sensitivity between ELISA and the cytotoxicity L929 bioassay. We concluded that whole blood culture is a sensitive method to determine the pro-inflammatory cytokine production in response to endotoxin stimuli in a relevant physiologic milieu. Our data indicate that this method provides appropriate information about the state of cellular immunity of the individual.

Total cytokine immunoassay: a more accurate method of cytokine measurement?

BACKGROUND

Cytokines signal the normal processes of inflammation and repair in all organs, yet the aberrant expression of these peptide mediators is associated with significant organ dysfunction. The accurate measurement of cytokines is therefore critical. In this study, we sought to investigate the alterations in cytokine expression early after trauma in humans using a new competitive binding immunoassay that measures both free and bound cytokine and compare this with standard enzyme-linked immunosorbent assay (ELISA), which measures only free cytokine.

METHODS

Peripheral blood was obtained from trauma patients at admission. Exclusion criteria were transfers, death within 24 hours, pregnancy, known acquired immunodeficiency syndrome, chemotherapy, transplant, or other chronic immune disorder. "Total" cytokine immunoassay was compared with ELISA for cytokines (interleukin [IL]-1, IL-6, and IL-10) measured in serum.

RESULTS

Cytokine concentrations measured by total immunoassay were significantly higher (10- to 500-fold increase) than those measured by ELISA, and correlation between the two methods was poor (r2 = 0.193 for IL-10). No significant differences in mean serum cytokine concentrations were noted between trauma patients and normal controls for IL-1 (56 vs. 37 pg/mL), IL-6 (16 vs. 25 pg/mL), and IL-10 (4 vs. 26 pg/mL) using the ELISA method. In contrast, trauma patients had significantly higher serum concentrations of IL-1 (3,320 vs. 1,470 pg/mL, p < 0.05), IL-6 (2,415 vs. 1,048 pg/mL, p < 0.05), and IL-10 (2,307 vs. 1,480 pg/mL, p < 0.05) at admission compared with normal controls using total cytokine immunoassays.

CONCLUSION

Cytokine measurements in peripheral blood in trauma patients and normal controls are significantly (10- to 500-fold) higher when using a total cytokine assay that measures both free and bound cytokine. Competitive immunoassays may be the method of choice when measuring endogenous cytokine levels in biologic fluids, and new normal ranges for cytokines must be established for future accurate research in critical care and trauma.

Measurement of cytokine secretion, intracellular protein expression, and mRNA in resting and stimulated peripheral blood mononuclear cells

Quantitation of cytokine production is a valuable adjunct to standard immunologic assays in defining several pathologic processes. Nevertheless, there is little agreement about which tissues should be assayed, which type of assay should be performed, and which stimulation protocol should be used. As these types of assays enter the clinical arena, there is need for standardization. There is also a need to maximize the amount of information which may be derived from a single sample. We compared secreted interleukin 4 (IL-4), IL-2, IL-6, tumor necrosis factor alpha (TNF-alpha), and gamma interferon proteins as measured by enzyme-linked immunosorbent assay with intracellular cytokine production (IL-2 and gamma interferon) as detected by flow cytometry and quantitative competitive PCR for IL-2, IL-4, TNF-alpha, and gamma interferon mRNA and cDNA. Results from unstimulated cells and cells stimulated with phorbol myristate acetate, phytohemagglutinin, and phorbol myristate acetate plus phytohemagglutin were compared. All three methodologies detected significant stimulation of cytokine production. The combination of phytohemagglutinin and phorbol myristate acetate was overall the most-potent stimulus.

A critical comparison of frequently used methods for the analysis of tumor necrosis factor-alpha expression by human immune cells

A variety of methods have been developed for the measurement of tumor necrosis factor (TNF)-alpha synthesis by immune cells. Here we have compared the results of the most common used methods, including in vitro stimulation of whole blood or peripheral blood mononuclear cell (PBMC) cultures with phytohaemagglutinin (PHA) or lipopolysaccharide (LPS) and RT-PCR analysis of TNF-alpha transcription in unstimulated PBMC. When we used EDTA treated blood samples we observed a significant correlation between the PHA and LPS stimulated TNF-alpha responses in whole blood or PBMC cultures. In contrast, TNF-alpha concentrations obtained from PHA and LPS stimulated whole blood cultures from citrate-treated blood did not show a correlation. We also found that the PHA stimulated TNF-alpha response was significantly higher in PBMC than in whole blood cultures, whereas the highest LPS stimulated TNF-alpha response was observed in citrate-treated blood. Moreover, the TNF-alpha response in both, citrate and EDTA treated whole blood cultures was significantly higher after LPS than after PHA stimulation. In contrast, in PBMC cultures the PHA stimulated TNF-alpha response was significantly higher than the LPS stimulated response. The results of RT-PCR analysis revealed a significant correlation with the PHA stimulated TNF-alpha response, both in whole blood assays and in PBMC cultures. In addition our results demonstrate that these different methods can only be compared when the influence of external factors such as the immediate processing of blood samples or the use of an appropriate anticoagulant and stimulant is considered.