Cell-mediated immune responses to mycobacterial antigens in patients with pulmonary tuberculosis and HIV infection

Lymphocyte proliferation and cytokine responses induced by a panel of mycobacterial antigens were compared in Portuguese donors with pulmonary tuberculosis (TB) with or without HIV co-infection, HIV⁺ patients and healthy Mantoux-positive controls. Control donors showed stronger proliferative responses than any of the patient groups, with secreted antigens (Mycobacterium tuberculosis (Mtb) 30 kD and short-term culture filtrate proteins (ST-CFP)), purified protein derivative (PPD) and Mtb H37Rv Sonicate (MtbS) inducing the strongest proliferation. Patients with pulmonary TB showed lower proliferation to PPD or to the 30-kD antigen. Responses to all the antigens (PPD, ST-CFP, MtbS, 70 kD, 65 kD, 38 kD, 30 kD and 10 kD) were higher in TB/HIV patients with CD4 counts 200 CD4⁺ T cells/mm³ compared with HIV alone (CD4 200 T cells/mm³), but were lost in both TB/HIV and HIV patients when CD4 counts fell below 200 T cells/mm³. Measurements of interferon-gamma (IFN-γ) in culture supernatants revealed that PPD, 30 kD, MtbS and ST-CFP induced the strongest Th1 response. Analysis of mRNA for IFN-γ, IL-4 and IL-10 confirmed that IFN-γ production was maintained in patients with pulmonary TB without any concomitant increase in IL-4 or IL-10 mRNA expression, although expression of IL-10 mRNA was increased if HIV infection was present. These results reveal that IFN-γ production is retained in pulmonary TB patients to a broad range of mycobacterial antigens, and that no switch to IL-4 production is seen even with HIV infection. Secreted antigens, and in particular ST-CFP, were the best inducers of IFN-γ secretion, confirming their role in protective responses to Mtb.     

Plasma antiviral activity and interferon-gamma production by superantigen-stimulated lymphocytes during normal human pregnancy

PROBLEM: Plasma interferon (IFN)-beta levels, lymphocyte responsiveness, and evaluation of the relationship between circulating antiviral activity (AA) and IFN-gamma production were studied in pregnant women and nonpregnant age-matched controls with the objective of elucidating the downregulation of IFN-gamma production in successful pregnancy. METHOD OF STUDY: In plasma and supernatants of peripheral blood mononuclear cell (PBMC) cultures, stimulated with staphylococcal enterotoxin A (SEA) superantigen, from 43 pregnant women with a history of normal pregnancy and 30 healthy nonpregnant age-matched controls, levels of AA were measured in a micromethod by inhibition of the cytopathic effect (CPE) caused by vesicular stomatitis virus (VSV) in the human amnionic cell line (WISH). RESULTS: Significantly higher plasma AA (60% was IFN-gamma and residual activity was acid-labile IFN-like) was present in pregnant women than controls. On the other hand, SEA-activated PBMCs from pregnant women produced significantly lower IFN-gamma levels than those of nonpregnant women. Furthermore, maternal plasma AA levels correlated negatively with IFN-gamma production by SEA-stimulated PBMCs. CONCLUSION: The hypothesis that successful pregnancy requires downregulation of IFN-gamma is only partially sustained, suggesting that the immunology of pregnancy is more complex and that murine and human pregnancy have different cytokine profiles.     

High endothelial-like venules in chronically inflamed periodontal tissues exchange polymorphs

A survey of 58 gingival biopsies revealed the presence of periodontal high endothelial-like venules (PHELVs) in chronically inflamed gingival tissues. PHELVs were found to exchange polymorphonuclear cells (PMNs) almost exclusively in advanced periodontitis, with PMNs greatly exceeding the number of mononuclear cells found in PHELVs (P less than 0.001). Electron microscopy confirmed the emigration of PMNs from these vessels. The enzyme histochemical and ultrastructural features as well as the 35SO4 uptake properties of PHELVs were similar to those of the well-characterized high endothelial venules (HEVs) of rat lymph nodes. It is generally accepted that HEVs in lymphoid tissues and inflammatory sites are specially adapted to assist in the emigration of lymphocytes. However, the observation of preferential PMN emigration in the apparent absence of lymphocyte exchange from PHELVs compels further investigation of other possible functions for HEVs. In relation to this, endothelial cells are capable of producing potent cytokines and inflammatory mediators which may contribute to the development of lesions, and the possibility is discussed that high endothelial cells are functionally adapted to enhance the production of such factors.     

Adjuvant-dependent modulation of Th1 and Th2 responses to immunization with beta-amyloid

The role of adjuvant on the T(h)1 and T(h)2 immune responses to Abeta-immunotherapy (Abeta(42 )peptide) was examined in wild-type mice. Fine epitope analysis with overlapping oligomers of the Abeta(42) sequence identified the 1-15 region as a dominant B cell epitope. The 6-20 peptide was recognized only weakly by antisera from mice administrated with Abeta(42) peptide formulated in complete Freund's adjuvant (CFA), alum or TiterMax Gold (TMG). However, mice immunized with Abeta(42) mixed with QS21 induced a significant antibody response to the 6-20 peptide. The only T cell epitope found was within the 6-28 sequence of Abeta(42). QS21 and CFA induced the strongest humoral response to Abeta, alum was intermediate, and TMG the weakest adjuvant. Analysis of antibody isotypes specific for Abeta indicates that alum induces primarily T(h)2-type immune response, whereas TMG, CFA and QS21 shift the immune responses toward a T(h)1 phenotype. Stimulation of splenocytes from Abeta-immunized mice with Abeta(40) peptide induced strikingly different cytokine expression profiles. QS21 and CFA induced significant IFN-gamma, IL-4 and tumor necrosis factor-alpha expression, whereas alum induced primarily IL-4 production. As T(h)1-type immune responses have been implicated in many autoimmune disorders, whereas T(h)2-type responses have been shown to inhibit autoimmune disease, the choice of adjuvant may be critical for the design of a safe and effective immunotherapy for Alzheimer's disease.     

Enhanced viral clearance in interleukin-18 gene-deficient mice after pulmonary infection with influenza A virus

T helper 1 driven immune responses facilitate host defence during viral infections. Because interleukin-18 (IL-18) mediates T helper 1 driven immune responses, and since mature IL-18 is up-regulated in human macrophages after influenza virus infection in vitro, it has been suggested that IL-18 plays an important role in the immune response to influenza. To determine the role of IL-18 in respiratory tract infection with influenza, IL-18 gene-deficient (IL-18(-/-)) and normal wildtype mice were intranasally inoculated with influenza A virus. Influenza resulted in an increase in constitutively expressed IL-18 in the lungs of wildtype mice. The clearance of influenza A was inhibited by IL-18, as indicated by reduced viral loads on day 8 and day 12 after infection in IL-18(-/-) mice. This enhanced viral clearance correlated with increased CD4(+) T-cell activation in the lungs as reflected by CD69 expression on the cell surface. Surprisingly, interferon-gamma (IFN-gamma) levels were similar in the lungs of IL-18(-/-) mice and wildtype mice. Intracellular IFN-gamma staining revealed similar expression levels in lung-derived natural killer cells, CD4(+) and CD8(+) T cells, indicating that IFN-gamma production is IL-18-independent during influenza virus infection. Tumour necrosis factor-alpha production by CD4(+) T cells was significantly lower in IL-18(-/-) mice than in wildtype mice. Our data indicate that endogenous IL-18 impairs viral clearance during influenza A infection.     

Reduced susceptibility to dextran sulphate sodium-induced colitis in the interleukin-2 heterozygous (IL-2) mouse

Summary Mice homozygous for an inactivation of the interleukin-2 (IL-2) gene develop a T-cell dependent colitis. Heterozygous (IL-2+/-) mice are clinically healthy but have been shown to express reduced levels of IL-2 in the colon. Splenocytes from the IL-2+/- mice had a poorer proliferative response to polyclonal T-cell activation and these mice have reduced numbers of intestinal regulatory T cells (CD4+ CD25+ cells) when compared to wild type mice. When exposed to dextran sulphate sodium (DSS) IL-2+/- mice showed a markedly reduced susceptibility to DSS-induced colitis. While DSS treatment caused a marked increase in both CD4+ and CD8+ colonic T cells expressing increased levels of IL-2, IL-4, and IL-10 in wild type mice none of these changes were seen in IL-2+/- mice. On the contrary, cytokine expression in intestinal T cells of IL-2+/- mice was actually reduced after DSS treatment. These results suggest that reduced levels of IL-2 leads to attenuated activation and function of intestinal T cells in IL-2+/- mice and a failure to react adequately to DSS exposure.     

Impeded Th1 CD4 memory T cell generation in chronic-persisting liver infection with Echinococcus multilocularis

Memory T cells of the CD4 lineage coordinate immune responses against pathogens via the antigen-induced secretion of potent effector cytokines. The efficacy of these responses is thought to depend on both the overall number of pathogen-specific memory T cells and the particular array of cytokines that these cells are programmed to secrete. It is unknown to what extent cellular immunity can be induced by Echinococcus multilocularis infection. To examine the immunological memory provided by the adaptive cellular immune system in control of the chronic-persisting infection, peripheral lymphocytes of patients with alveolar echinococcosis (AE) were studied ex vivo. Stimulation of memory cells was performed with E. multilocularis vesicular fluid, purified protein derivative as recall antigen and phytohemagglutinin. Cytomegalovirus latency served as disease control. Frequencies of circulating CD4(+) T cells secreting IFN-gamma, IL-2, tumor necrosis factor-alpha, IL-4, IL-5 and IL-10 were determined by both cytokine flow cytometry and ELISPOT assays. Most strikingly, in chronic AE the frequencies of E. multilocularis antigen-specific cells committed to T(h)1-cytokine production were low (mean 0.5% of CD4(+) T cells). However, an E. multilocularis-specific response of CD4(+) T cells at frequencies of >/=0.1% was detected in the majority of AE patients (68%). Low numbers of cells committed to T(h)1 cytokine secretion were invariably seen in patients with active and inactive disease. Interestingly, the number of specific CD4(+) memory T cells was not increased in cured AE patients after complete surgical removal of the metacestode. Hyporesponsiveness during the chronic helminth infection was E. multilocularis specific. Thus, our results demonstrate that antigen-specific memory function against E. multilocularis is markedly different from that against viral or bacterial pathogens. Whether the antigen-specific cellular hyporesponsiveness with impeded T(h)1 CD4(+) memory T cell generation is a cause or a result of the progressive metacestode activity remains to be determined.