The diversity of contemporary swine influenza virus (SIV) strains impedes effective immunization of swine herds. Mucosally delivered, attenuated virus vaccines are one approach with potential to provide broad crossprotection. Reverse genetics-derived H3N2 SIV virus with truncated NS1 (NS1Δ126 TX98) is attenuated and immunogenic when delivered intranasally in young pigs. We analyzed T-cell priming and cross-protective efficacy in weanling piglets after intranasal inoculation with NS1Δ126 TX98 versus wild type TX98. In vivo replication of the truncation mutant was minimal compared to the wild type virus. T-cell responses were greater in magnitude in pigs infected with the wild type virus in in vitro restimulation assays. According to the expression of activation marker CD25, peripheral T cell recall responses in NS1Δ126 TX98 infected pigs were minimal. However, intracellular IFN-γ data indicate that the attenuated virus induced virus-specific CD4 + CD8 -, CD4 + CD8 + , CD4 -CD8 + , and γδ T cells within 28 days. The IFN-γ response appeared to contract, as responses were reduced at later time points prior to challenge. CD4 + CD8 + cells isolated 5 days after heterosubtypic H1N1 challenge (day 70 overall) showed an elevated CD25 response to virus restimulation. Pigs previously infected with wild type TX98 were protected from replication of the H1N1 challenge virus. Vaccination with NS1Δ126 TX98 was associated with significantly lower levels of Th1-associated cytokines in infected lungs but provided partial cross-protection against the H1N1 challenge. These results demonstrate that NS1Δ SIV vaccines can elicit cell-mediated cross-protection against antigenically divergent strains. The diversity of contemporary swine influenza virus (SIV) strains impedes effective immunization of swine herds. Mucosally delivered, attenuated virus vaccines are one approach with potential to provide broad cross-protection. Reverse genetics-derived H3N2 SIV virus with truncated NS1 (NS1 126 TX98) is attenuated and immunogenic when delivered intranasally in young pigs. We analyzed T-cell priming and cross-protective efficacy in weanling piglets after intranasal inoculation with NS1 126 TX98 versus wild type TX98. In vivo replication of the truncation mutant was minimal compared to the wild type virus. T-cell responses were greater in magnitude in pigs infected with the wild type virus in in vitro restimulation assays. According to the expression of activation marker CD25, peripheral T cell recall responses in NS1 126 TX98 infected pigs were minimal. However, intracellular IFN-␥ data indicate that the attenuated virus induced virus-specific CD4 + CD8 -, CD4 + CD8 + , CD4 -CD8 + , and ␥␦ T cells within 28 days. The IFN-␥ response appeared to contract, as responses were reduced at later time points prior to challenge. CD4 + CD8 + cells isolated 5 days after heterosubtypic H1N1 challenge (day 70 overall) showed an elevated CD25 response to virus restimulation. Pigs previously infected with wild type TX98 were protected from replicatio...
Live-attenuated influenza virus (LAIV) prime-boost vaccination previously conferred protection against heterologous H3N2 swine influenza challenge, including in piglets with maternally derived antibodies (MDA). Conversely, a whole-inactivated virus (WIV) vaccine was associated with enhanced disease. This study was aimed at identifying immune correlates of cross-protection. Piglets with and without MDA received intramuscular adjuvanted WIV or intranasal LAIV, and were challenged with heterologous H3N2. WIV induced cross-reactive IgG, inhibited by MDA, and a moderate T cell response. LAIV elicited mucosal antibodies and T cells cross-reactive to the heterologous challenge strain. The presence of MDA at LAIV vaccination blocked lung and nasal antibody production, but did not interfere with T cell priming. Even without mucosal antibodies, MDA-positive LAIV vaccinates were protected, indicating a likely role for T cells. Based on the data, one LAIV dose can induce cell-mediated immunity against antigenically divergent H3N2 influenza virus despite passive antibody interference with humoral immune responses.
The ability of porcine reproductive and respiratory syndrome virus (PRRSV) to suppress T cell expression of CD25 (alpha chain of interleukin [IL]-2 receptor), interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) was determined by flow cytometry in naive porcine T cells in response to mitogen (concanavalin A) and cytokine inducers (phorbol 12-myristate 13-acetate plus ionomycin [PMA/I]). Four PRRSV isolates of varying clinical virulence and three different types of porcine myeloid antigen-presenting cells (APCs) were used. T cells cultured with monocytes infected with virulent PRRSV (VR-2385, SDSU-73, and VR-2332), but not with a vaccine strain (Ingelvac PRRS MLV; Boehringer Ingelheim Vetmedica, St. Joseph, MO), demonstrated significantly reduced CD25 expression (%CD25(+)) and IFN-gamma expression (%IFN-gamma (+)) compared with T cells incubated with uninoculated monocyte cultures. T cells cultured with monocytes infected with all four PRRSV isolates demonstrated significantly reduced %TNF-alpha (+). The significant reduction of %CD25(+), %IFN-gamma (+), and %TNF-alpha (+) was not detected in T cells cultured with monocyte-derived macrophages (MDMs) and immature monocyte-derived dendritic cells (MDCs) infected with any PRRSV isolates. Heat-inactivated PRRSV did not induce significantly reduced T cell responses in any APC cultures. The reduction of T cell response in monocyte cultures was not due to PRRSV-induced T cell death. Gene expression of IL-10 detected by semiquantitative reverse transcriptase-polymerase chain reaction was significantly increased in virulent PRRSV-infected monocyte cultures after PMA/I, but not concanavalin A, stimulation compared with IL-10 gene expression from uninoculated monocyte cultures. Increased IL-10 gene expression contributed to significantly reduced %IFN-gamma (+) and %TNF-alpha (+), but not %CD25(+), as determined by IL-10 neutralization assay. This study reports that PRRSV has the ability to suppress T cell responses. The suppressive ability of PRRSV is associated with viral virulence and is mediated by virus-infected monocytes, but not by virus-infected MDMs and immature MDCs.
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