Characterization of the HCMV-Specific CD4 T Cell Responses that Are Associated with Protective Immunity

Most humans become infected with human cytomegalovirus (HCMV). Typically, the immune system controls the infection, but the virus persists and can reactivate in states of immunodeficiency. While substantial information is available on the contribution of CD8 T cells and antibodies to anti-HCMV immunity, studies of the T_H1, T_H2, and T_H17 subsets have been limited by the low frequency of HCMV-specific CD4 T cells in peripheral blood mononuclear cell (PBMC). Using the enzyme-linked Immunospot^® assay (ELISPOT) that excels in low frequency measurements, we have established these in a sizable cohort of healthy HCMV controllers. Cytokine recall responses were seen in all seropositive donors. Specifically, interferon (IFN)-γ and/or interleukin (IL)-17 were seen in isolation or with IL-4 in all test subjects. IL-4 recall did not occur in isolation. While the ratios of T_H1, T_H2, and T_H17 cells exhibited substantial variations between different individuals these ratios and the frequencies were relatively stable when tested in samples drawn up to five years apart. IFN-γ and IL-2 co-expressing polyfunctional cells were seen in most subjects. Around half of the HCMV-specific CD4 cells were in a reversible state of exhaustion. The data provided here established the T_H1, T_H2, and T_H17 characteristic of the CD4 cells that convey immune protection for successful immune surveillance against which reactivity can be compared when the immune surveillance of HCMV fails.     

A Novel ELISPOT Assay to Quantify HLA‐Specific B Cells in HLA‐Immunized Individuals

Quantification of the humoral alloimmune response is generally achieved by measuring serum HLA antibodies, which provides no information about the cells involved in the humoral immune response. Therefore, we have developed an HLA‐specific B‐cell ELISPOT assay allowing for quantification of B cells producing HLA antibodies. We used recombinant HLA monomers as target in the ELISPOT assay. Validation was performed with human B‐cell hybridomas producing HLA antibodies. Subsequently, we quantified B cells producing HLA antibodies in HLA‐immunized individuals, non‐HLA‐immunized individuals and transplant patients with serum HLA antibodies. B‐cell hybridomas exclusively formed spots against HLA molecules of corresponding specificity with the sensitivity similar to that found in total IgG ELISPOT assays. HLA‐immunized healthy individuals showed up to 182 HLA‐specific B cells per million total B cells while nonimmunized individuals had none. Patients who were immunized by an HLA‐A2‐mismatched graft had up to 143 HLA‐A2‐specific B cells per million total B cells. In conclusion, we have developed and validated a highly specific and sensitive HLA‐specific B‐cell ELISPOT assay, which needs further validation in a larger series of transplant patients. This technique constitutes a new tool for quantifying humoral immune responses.     

Diversion of intestinal flow decreases the numbers of interleukin 4 secreting and interferon gamma secreting T lymphocytes in small bowel mucosa

BACKGROUND/AIMS: The intestinal immune system faces large amounts of antigens, and its regulation is tightly balanced by cytokines. In this study, the effect of intestinal flow diversion on spontaneous secretion of interleukin (IL)-4 and interferon (IFN)- gamma was analysed. METHODS: Eight patients (two with Crohn's disease, four with ulcerative colitis, and two with previous colon cancer) carrying a double lumen small bowel stoma after a total colectomy procedure were included in the study. For each patient, eight biopsy samples were taken endoscopically from both the diverted and non-diverted part of the small bowel. Intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs) were isolated separately and assayed for numbers of cells spontaneously secreting IL-4 and/or IFN-gamma by an ELISPOT technique. RESULTS: Compared with the non-diverted mucosa, a significant decrease in the number of spontaneously IFN-gamma secreting CD3 lymphocytes was observed in the diverted small bowel mucosa among both IELs (p = 0.008) and LPLs (p = 0.007). The same results, although less significant, were obtained for IL-4, especially in LPLs (p = 0.01). CONCLUSION: The intestinal content influences the spontaneous secretion of IFN-gamma and IL-4 by intestinal lymphocytes. These results could help to elucidate the anti-inflammatory role of split ileostomy in patients suffering from inflammatory bowel diseases.     

HLA-A*0201 restricted CD8+ T-lymphocyte responses to malaria: identification of new Plasmodium falciparum epitopes by IFN-gamma ELISPOT

The role of antigen specific CD8+ T-lymphocytes in mediating protection against sporozoite-induced malaria has been well established in murine models. In humans, indirect evidence has accumulated suggesting a similar protective role for antigen-specific CD8+ T-lymphocytes. Nevertheless, the low frequency of circulating specific cells together with the lack of sensitive methods to quantify them has hampered the direct assessment of their function. Using a combination of short-term cell culture and IFN-gamma ELISPOT, we studied CD8+ T-lymphocyte responses to a panel of HLA-A*0201 binding peptides. In addition to confirming the response to already described epitopes, we also identified five new CD8+ T-lymphocyte epitopes. These epitopes are presented in pre-erythrocytic stages gene products of Plasmodium falciparum 7G8 strain and correspond to the following protein segments: circumsporozoite (CS) 64-72, 104-113, 299-308 and 403-411; liver stage antigen (LSA-1) repeat region; sporozoite surface protein 2 or thrombospondin related anonymous protein (SSP2/TRAP) 78-88 and 504-513. Four of these peptides are conserved amongst all published sequences of P. falciparum strains. We conclude that the modified IFN-gamma ELISPOT assay is a sensitive technique to monitor antigen-specific CD8+ T-lymphocyte responses in human malaria which may help in the improvement and assessment of the efficacy of malaria subunit vaccines.     

Screening for tuberculosis among 2381 household contacts of sputum-smear-positive cases in The Gambia

Contact investigation is a key component of tuberculosis (TB) control in developed, but not developing, countries. We aimed to measure the prevalence of TB among household contacts of sputum-smear-positive TB cases in The Gambia and to assess the sensitivity of an enzyme-linked immunospot (ELISPOT) assay in this regard. Household contacts of adult smear-positive TB patients were assessed by questionnaire, purified protein derivative (PPD) skin test, ELISPOT assay, physical examination, chest X-ray and sputum/gastric aspirate. Thirty-three TB cases were identified from 2174 of 2381 contacts of 317 adult smear-positive pulmonary TB patients, giving a prevalence of 1518/100000. The cases identified tended to have milder disease than those passively detected. The sensitivity of ESAT-6/CFP-10 ELISPOT test as a screening test for TB disease was estimated as 71%. Fifty-six per cent of contacts with a PPD skin test result >or=10mm induration had detectable responses to ESAT-6/CFP-10 by ELISPOT; 11% with a negative PPD skin test (<10mm) had a positive ESAT-6/CFP-10 response. Active screening for TB among contacts of TB patients may have a role in TB control in The Gambia. These individuals are a high-risk group, and the disease identified is less advanced than that found through passive case detection. An ELISPOT assay was relatively insensitive as a screening test for TB.     

Cytokine-specific ELISPOT assay single cell analysis of IL-2, IL-4 and IL-6 producing cells

In order to assess cytokine-producing cells at the single cell level, the cytokine-specific ELISPOT assay has proven to be an important and sensitive method. The purpose of this study was to adapt this method to elucidate individual cells producing murine IL-2, IL-4 or IL-6. In order to establish these cytokine-specific ELISPOT assays, IL-2-, IL-4- and IL-6-specific cDNA transfected myeloma cell lines, e.g., X63-Ag8-653 X2, X63-Ag8-653 X4 and X63-Ag8-653 X6, respectively, were used as specific cytokine-producing cells. In the IL-2 ELISPOT assay, the coating reagent, monoclonal antibody (mAb) rat IgG2a anti-mouse IL-2 (CR #40014) was used while rabbit IgG polyclonal anti-mouse IL-2 was employed for detection of IL-2 spot forming cells (SFC). The mAbs anti-mouse IL-4, BVD4-1D11 and BVD6-24G2 were selected as capture and detection antibodies for enumeration of IL-4 SFC. For the IL-6 ELISPOT assay, anti-mouse IL-6 (MP5-20F3) mAb was used for coating and MP5-32C11 mAb was used for detection of IL-6 SFC. When IL-2 producing X63-Ag8-653 X2 cells were subjected to these three different ELISPOT assays, IL-2-specific SFC were only noted with the IL-2 ELISPOT system. In the case of IL-4 SFC, only X63-Ag8-653 X4 cells formed specific spots using the tandem of BVD4-1D11 and BVD6-24G2 mAbs. IL-6-specific spots developed in MP5-20F3 mAb pre-coated wells containing X63-Ag8-653 X6 cells, when developed with mAb anti-IL-6 (MP5-32C11). Addition of cycloheximide (50 μg/ml) inhibited formation of IL-2, IL-4 and IL-6 SFC by approximately 90%. When an unrelated mAb was used as detection antibody in these three different cytokine-specific ELISPOT assays, IL-2-, IL-4-and IL-6-specific SFC were not detected. Further, when concanavalin A stimulated T cells from Peyer's patch of normal mice were subjected to the respective cytokine-specific ELISPOT assay, IL-2, IL-4 and IL-6 SFC were enumerated. These results have shown that cytokine-specific IL-2, IL-4 and IL-6 ELISPOT assays have now been established and will allow analysis of the frequency of cytokine-secreting cells at the single cell level.     

Feasibility of commercial interferon-γ-based methods for the diagnosis of latent Mycobacterium tuberculosis infection in Finland, a country of low incidence and high bacille Calmette–Guérin vaccination coverage

The performances of the QuantiFERON-TB Gold in Tubes (QFGT), T SPOT-TB (ELISPOT) and the Mantoux test were compared for the diagnosis of latent tuberculosis infection in Finland, a country of low tuberculosis incidence. In Cohort A (16 students), freshly isolated peripheral blood mononuclear cells (PBMCs), and in Cohort B (21 school children), cryopreserved PBMCs, were used for the ELISPOT assay. Cryopreservation of cells in fetal calf serum, but not in serum-free medium, produced false-positive results. Discrepancies between the results of the assays were observed. It was concluded that the accuracy of these ex-vivo methods needs additional evaluation.     

一种IFN-γ ELISPOT检测方法的建立

目的:建立检测一种融合蛋白疫苗诱导特异性细胞免疫的ELISPOT实验方法,通过分析免疫小鼠分泌IFN-γ的水平,评价疫苗诱导的细胞免疫应答效应.方法:以融合蛋白疫苗免疫C57BL/6小鼠,14天后加强免疫一次,于第28天无菌取脾,分离脾淋巴细胞,计数并调整细胞浓度,在已包被好的ELISPOT板中分别加入细胞悬液和刺激肽进行刺激培养.裂解细胞,依次加入酶标二抗、底物、显色液,在ELISPOT读板仪进行斑点计数和分析.结果:ELISPOT检测结果与动物免疫途径、细胞培养时间、细胞密度、肽浓度等条件密切相关.实验结果证明:采用皮下注射的免疫途径,免疫效果最佳;小鼠脾淋巴细胞浓度为4×105个/孔,加入1 μg/孔的刺激肽刺激培养24～48小时的条件下,产生的特异性斑点数最多,本底干扰小,有利于结果判断.结论:实验建立了IFN-γ ELISPOT检测方法,可用于该融合蛋白疫苗细胞免疫研究.     

BK Virus‐Specific Immunity Kinetics: A Predictor of Recovery From Polyomavirus BK‐Associated Nephropathy

Impaired BKV‐specific immunity is associated with development of BKV‐associated nephropathy. Suitable immunological parameters to identify patients at risk, however, are still debated. We monitored 18 kidney‐transplant recipients through the course of self‐limited BKV‐reactivation (n = 11) and BKV‐associated nephropathy (n = 7). BKV‐specific cellular immunity directed to nonstructural small and Large T‐antigen, and structural VP1–3 was analyzed in an interferon‐γ Elispot assay. BKV‐specific IgM and IgG were measured using an enzyme‐linked immunosorbent assay simultaneously. BKV‐specific cellular immunity directed to five BKV‐proteins increased significantly from diagnosis to resolution of BKV‐reactivation (p < 0.001). Patients with self‐limited BKV‐reactivation developed BKV‐specific T cells without therapeutic interventions, and cleared BKV‐reactivation within a median period of 1 month. Patients with BKV‐associated nephropathy, however, showed BKV‐specific T cells after a median period of 5 months after therapeutic interventions only, and cleared BKV‐reactivation after a median period of 8 months. Anti‐structural T cells were detected earlier than anti‐nonstructural T cells, which coincided with BKV‐clearance. Patients with BKV‐associated nephropathy showed the highest frequencies of BKV‐specific T cells at recovery, the highest increase in BKV‐specific IgG and persistence of increased IgM levels (p < 0.05). Our results suggest prognostic values of BKV‐specific immune monitoring to identify those patients at risk of BKV‐associated nephropathy and to aid in the management of therapeutic interventions.     

A novel assay to measure B cell responses to keyhole limpet haemocyanin vaccination in healthy volunteers and subjects with systemic lupus erythematosus

The aim of the study was to characterize performance of a complementary set of assays to measure antigen-specific immune responses in subjects immunized with a neoantigen. Healthy volunteers (HV) (n = 8) and patients with systemic lupus erythematosus (SLE) (n = 6) were immunized with keyhole limpet haemocyanin (KLH) on days 1 and 29. Serum antibodies were detected using a flow cytometric bead array (CBA) that multiplexed the KLH response alongside pre-existing anti-tetanus antibodies. Peripheral blood mononuclear cells were studied by B cell ELISPOT. These assays were built upon precedent assay development in cynomolgus monkeys, which pointed towards their utility in humans. Primary anti-KLH IgG responses rose to a mean of 65–93-fold above baseline for HV and SLE patients, respectively, and secondary responses rose to a mean of 260-170-fold above baseline. High levels of anti-tetanus IgG were detected in pre-immunization samples and their levels did not change over the course of study. Anti-KLH IgG1-4 subclasses were characterized by a predominant IgG1 response, with no significant differences in subclass magnitude or distribution between HV and SLE subjects. Anti-KLH IgM levels were detectable, although the overall response was lower. IgM was not detected in two SLE subjects whodid generate an IgG response. All subjects responded to KLH by B cell ELISPOT, with no significant differences observed between HV and SLE subjects. The CBA and B cell ELISPOT assays reliably measured anti-KLH B cell responses, supporting use of this approach and these assays to assess the pharmacodynamic and potential safety impact of marketed/investigational immune-therapeutics.