Strong purified protein derivative responses are associated with poor mycobacterium inhibition in latent TB

The tuberculin skin test (TST) using purified protein derivative (PPD) of Mycobacterium tuberculosis is traditionally used to diagnose latent tuberculosis (TB) infection (LTBI). However, LTBI diagnosis by peripheral blood mononuclear cell (PBMC) interferon (IFN)-gamma responses to M. tuberculosis-specific antigens, early secreted antigenic target 6 kDa (ESAT-6) and culture filtrate protein (CFP)-10 has greater specificity. We investigated the difference in antimycobacterium cellular immunity in TB contacts who were strong TST reactors but nonresponsive to the ESAT-6/CFP-10 assay compared with those with concordant results. Healthy TB contacts were tested using the above two assays and mycobacterium survival was measured after co-culture of infected macrophages with their PBMCs. Whether PPD reactivity was tested by TST or by PBMC-specific IFN-gamma responses, strongly PPD-reactive TB contacts without ESAT-6/CFP-10 responsiveness showed significantly better mycobacterium inhibition activity than ESAT-6/CFP-10-responsive TB contacts with the same PPD reactivity. In the former group, stronger PPD reactivity was associated with improved mycobacterium killing, whereas ESAT-6/CFP-10 responders showed the opposite result. PPD-reactive ESAT-6/CFP-10-nonresponsive TB contacts in our population may have had protective immunity related to prior mycobacterium exposure. ESAT-6/CFP10-responsive TB contacts are more likely to have LTBI and, in this group, strong PPD reactivity may paradoxically be associated with poor mycobactericidal activity.

Interleukin-4 and its alternatively spliced variant (IL-4delta2) in patients with atopic asthma

The interleukin-4 (IL-4) splice variant (IL-4delta2) is known to antagonize many biological activities of IL-4, and this challenges our understanding of the role of IL-4 in asthma. Studies that have used nonspecific antibodies, probes, and/or primers to quantify IL-4 in clinical samples would not have distinguished the expression of IL-4 from IL-4delta2. This is the first study to examine patients with chronic asthma and atopy for IL-4delta2 mRNA in their peripheral blood mononuclear cells without antigen stimulation, using a quantitative nested reverse-transcription polymerase chain reaction (RT-PCR) protocol. The median IL-4 mRNA copy number in cells from the patients with asthma was 2.8 logs higher than in a comparator group of patients with tuberculosis (p = 0.0005) and 4.5 logs higher (p = 0.0004) than in healthy control subjects. In contrast, IL-4delta2 expression in cells from patients with asthma was similar to that seen in cells from patients with tuberculosis. Hence, the median ratio of IL-4 to IL-4delta2 was 500-fold higher in the patients with asthma when compared with either patients with tuberculosis or healthy control subjects. The relative expression of IL-4 and IL-4delta2 may be a reason for the functional diversity of Th2 cells in different clinical conditions, and a hitherto unexplored mechanism for the pulmonary pathology in patients with atopic asthma.

Il-4 influences apoptosis of mycobacterium-reactive lymphocytes in the presence of TNF-alpha

T cell apoptosis is associated with defective cell-mediated effector functions in several infectious diseases. In tuberculosis, there is evidence that T cell apoptosis may be cytokine mediated, but the mechanisms are not clearly understood. Type 2 cytokines have recently been associated with disease extent in human tuberculosis, but they have not previously been linked to apoptosis in mycobacterium-reactive T cells. This study presents evidence that PBLs from healthy donors respond to sonicated Mycobacterium tuberculosis Ags with increased IL-4 gene activation, CD30 expression, and apoptosis. The changes were significantly greater than those observed when cells were stimulated with Ags from nonpathogenic Mycobacterium vaccae. A hypothesis linking these observations was tested. CD30 expression and TNF-alpha-mediated lymphocyte apoptosis were both down-regulated by inhibiting IL-4 in this model. TNFR-associated factor 2 (TRAF2) expression was down-regulated in CD30(+) cells, and addition of anti-TNF-alpha Ab significantly reduced apoptosis in the CD30(+) but not the CD30(-) population. These observations support the hypothesis that increased IL-4 expression in M. tuberculosis-activated lymphocytes promotes CD30 expression, which sensitizes the lymphocytes to TNF-alpha-mediated apoptosis via TRAF2 depletion. This may be one mechanism by which IL-4 is associated with immunopathological consequences in human tuberculosis.

High levels of mRNA encoding IL-4 in unstimulated peripheral blood mononuclear cells from tuberculosis patients revealed by quantitative nested reverse transcriptase-polymerase chain reaction; correlations with serum IgE levels

The dominant view has been that there is little or no activation of Type 2 cytokine production in human tuberculosis. A novel approach to quantitative nested reverse transcriptase-polymerase chain reaction has revealed that this conclusion was based on technical inadequacies of earlier studies, particularly the failure to discriminate between IL-4 and the IL-4 splice variant, IL4delta2. A new approach reveals that the largest cytokine change in tuberculosis is a 1-2 log increase in copy number for mRNAs encoding IL-4 and IL-13, accompanied by a small decrease in expression of mRNA encoding interferon-gamma. The increased IL-4 level correlates with disease severity and with serum levels of IgE and soluble CD30, and may be attributable to the recently observed increase in conversion of cortisone into cortisol in tuberculous lesions. The implications of these findings for pathogenesis, vaccine design and immunotherapy are discussed, as effective reagents will need to downregulate this inappropriate Th2 component.

Type 2 cytokine gene activation and its relationship to extent of disease in patients with tuberculosis

The extent of type 2 cytokine gene expression in patients with pulmonary tuberculosis (TB) was studied by use of quantitative nested reverse-transcription polymerase chain reaction on freshly isolated peripheral blood mononuclear cells. Interleukin (IL)-4 and IL-13 mRNA expression was significantly greater in patients-median mRNA copy numbers were 1.7 and 1.1 log10 higher, respectively-than in matched tuberculin-positive control subjects. Significant correlations with radiologic extent of disease and serum IgE levels supported the biologic significance of these results. Interferon-gamma mRNA copy numbers exceeded those of type 2 cytokines but were only marginally lower in patients than in control subjects. Gene expression of an IL-4 splice variant (IL-4delta2) was bimodally distributed in both patient and control groups. Patients with greater IL-4delta2 expression also expressed more IL-4 mRNA and had more extensive disease. Type 2 cytokines are associated with immunopathologic changes in TB patients but could be a cause or consequence of disease.

A sensitive, non-radioactive quantitative method for measuring IL-4 and IL-4delta2 mRNA in unstimulated cells from multiple clinical samples, using nested RT-PCR

Measurements of IL-4 mRNA directly from clinical samples are technically difficult as IL-4 is a low copy number cytokine. Moreover, most existing studies involving RT-PCR are confused by the use of primers which simultaneously amplify cDNA of IL-4 and its splice-variant (IL-4delta2). We describe a sensitive nested RT-PCR method to quantify mRNA expression of IL-4 and IL-4delta2 separately. It involves a simple method of generating cRNA standards without cloning. The use of external synthetic RNA standards, for which we validate that amplification kinetics are equivalent to the target, obviates the need for multiple sample dilutions. The assay is sensitive enough to measure IL-4 and IL-4delta2 mRNA expression in unstimulated PBMCs of normal subjects, and the reproducibility and throughput make this assay suitable for use in clinical studies with multiple samples.