Dissecting the T Cell Response: Proliferation Assays vs. Cytokine Signatures by ELISPOT.

Chronic allograft rejection is in part mediated by host T cells that recognize allogeneic antigens on transplanted tissue. One factor that determines the outcome of a T cell response is clonal size, while another is the effector quality. Studies of alloimmune predictors of transplant graft survival have most commonly focused on only one measure of the alloimmune response. Because differing qualities and frequencies of the allospecific T cell response may provide distinctly different information we analyzed the relationship between frequency of soluble antigen and allo-antigen specific memory IFN-g secreting CD4 and CD8 T cells, their ability to secrete IL-2, and their proliferative capacity, while accounting for cognate and bystander proliferation. The results show proliferative responses primarily reflect on IL-2 production by antigen-specific T cells, and that proliferating cells in such assays entail a considerable fraction of bystander cells. On the other hand, proliferation (and IL-2 production) did not reflect on the frequency of IFN-γ producing memory cells, a finding particularly accentuated in the CD8 T cell compartment. These data provide rationale for considering both frequency and effector function of pre-transplant T cell reactivity when analyzing immune predictors of graft rejection.

Impaired plasmacytoid dendritic cell (PDC)-NK cell activity in viremic human immunodeficiency virus infection attributable to impairments in both PDC and NK cell function.

Human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infections impair plasmacytoid dendritic cell (PDC) and natural killer (NK) cell subset numbers and functions, though little is known about PDC-NK cell interactions during these infections. We evaluated PDC-dependent NK cell killing and gamma interferon (IFN-gamma) and granzyme B production, using peripheral blood mononuclear cell (PBMC)-based and purified cell assays of samples from HCV- and HIV-infected subjects. CpG-enhanced PBMC killing and IFN-gamma and granzyme B activity (dependent on PDC and NK cells) were impaired in viremic HIV infection. In purified PDC-NK cell culture experiments, CpG-enhanced, PDC-dependent NK cell activity was cell contact and IFN-alpha dependent, and this activity was impaired in viremic HIV infection but not in HCV infection. In heterologous PDC-NK cell assays, impaired PDC-NK cell killing activity was largely attributable to an NK cell defect, while impaired PDC-NK cell IFN-gamma-producing activity was attributable to both PDC and NK cell defects. Additionally, the response of NK cells to direct IFN-alpha stimulation was defective in viremic HIV infection, and this defect was not attributable to diminished IFN-alpha receptor expression, though IFN-alpha receptor and NKP30 expression was closely associated with killer activity in viremic HIV infection but not in healthy controls. These data indicate that during uncontrolled HIV infection, PDC-dependent NK cell function is impaired, which is in large part attributable to defective IFN-alpha-induced NK cell activity and not to altered IFN-alpha receptor, NKP30, NKP44, NKP46, or NKG2D expression.

Accessory cell dependent NK cell mediated PBMC IFN-gamma production is defective in HIV infection.

HCV and HIV infections impair dendritic cell function. We evaluated the impact of HCV, HIV, and HCV-HIV infection on MDC-NK interactions by analyzing CD3 depleted PBMC for NK cell IFN-gamma in response to IL-12 or poly (I:C). Purified MDC and NK cells were analyzed for TLR ligand-dependent, MDC-dependent NK activity. In HIV infection, IFN-gamma production by CD3 depleted PBMC was reduced in response to poly (I:C), while response to IL-12 was intact in HCV and HIV infections. Poly (I:C) induced activity was dependent on MDC and partially dependent on IL-12, consistent with accessory cell help. In purified MDC-NK co-cultures, MDC dependent NK IFN-gamma and Granzyme B was intact in both HCV and HIV infections, while MDC numerical defects were observed in HIV infection. These data indicate that during viral infection with HIV, accessory cell dependent NK function in the periphery is impaired. This impairment may be related to the identified MDC numerical defect.

Hepatitis C virus-specific T-cell gamma interferon and proliferative responses are more common in perihepatic lymph nodes than in peripheral blood or liver.

The activation state, differentiation state, and functions of liver lymphocytes and perihepatic lymph nodes during chronic hepatitis C virus (HCV) infection are not well understood. Here, we performed phenotypic and functional analyses of freshly prepared lymphocytes isolated from the livers, perihepatic lymph nodes, and peripheral blood compartments of chronic HCV-infected and disease control subjects with end-stage liver disease undergoing liver transplantation. We measured lymphocyte subset frequency and memory T-cell gamma interferon (IFN-gamma) and proliferative responses to HCV peptide and control viral antigens in direct ex vivo assays. We found higher frequencies of CD4 cells in the lymph node compartment than in the other compartments for both HCV-infected and disease control subjects. Lymph node CD4 and CD8 cells less commonly expressed the terminal differentiation marker CD57, a finding consistent with an earlier differentiation state. In HCV-infected subjects, HCV-specific IFN-gamma-producing and proliferative responses were commonly observed in the lymph node fraction, while they were uncommonly observed in the peripheral blood or liver fractions. In contrast, control viral CD4 protein antigen and CD8 peptide antigen-specific IFN-gamma responses were commonly observed in the periphery and uncommonly observed in the lymph nodes of these same subjects. These findings are consistent with a selective defect in HCV-specific T-cell effector function or distribution in patients with advanced chronic HCV infection. The high frequency of HCV-reactive T cells in perihepatic lymph nodes indicates that a failure to generate or sustain T-lymphocyte HCV reactivity is not responsible for the paucity of functional cells even in end-stage liver disease.

TLR ligand-dependent activation of naive CD4 T cells by plasmacytoid dendritic cells is impaired in hepatitis C virus infection.

Chronic hepatitis C virus (HCV) infection is characterized by diminished numbers and function of HCV-reactive T cells and impaired responses to immunization. Because host response to viral infection likely involves TLR signaling, we examined whether chronic HCV infection impairs APC response to TLR ligand and contributes to the origin of dysfunctional T cells. Freshly purified myeloid dendritic cells (MDC) and plasmacytoid DC (PDC) obtained from subjects with chronic HCV infection and healthy controls were exposed to TLR ligands (poly(I:C), R-848, or CpG), in the presence or absence of cytokine (TNF-alpha or IL-3), and examined for indices of maturation and for their ability to activate allogeneic naive CD4 T cells to proliferate and secrete IFN-gamma. TLR ligand was observed to enhance both MDC and PDC activation of naive CD4 T cells. Although there was increased CD83 and CD86 expression on MDC from HCV-infected persons, the ability of MDC to activate naive CD4 T cells in the presence or absence of poly(I:C) or TNF-alpha did not differ between HCV-infected and healthy control subjects. In contrast, PDC from HCV-infected persons had reduced activation marker (HLA-DR) and cytokine (IFN-alpha) expression upon R-848 stimulation, and these were associated with impaired activation of naive CD4 T cells. These data indicate that an impaired PDC responsiveness to TLR ligation may play an important role in the fundamental and unexplained failure to induce new T cell responses to HCV Ags and to other new Ags as a consequence of HCV infection.