Reduction of CD4+ and CD8+ T lymphocytes during febrile periods in horses experimentally infected with equine infectious anemia virus

CD4+ T lymphocyte responses to viruses and virus-relevant stimuli in teleost fish

Fish diseases caused by viruses are a major threat to aquaculture. Development of disease protection strategies for sustainable fish aquaculture requires a better understanding of the immune mechanisms involved in antiviral defence. The innate and adaptive arms of the vertebrate immune system collaborate to mount an effective defence against viral pathogens. The T lymphocyte components of the adaptive immune system, comprising two major classes (helper T, Th or CD4+ and cytotoxic T lymphocytes, CTLs or CD8+ T cells), are responsible for cell-mediated immune responses. In particular, CD4+ T cells and their different subsets orchestrate the actions of various other immune cells during immune responses, making CD4+ T cells central drivers of responses to pathogens and vaccines. CD4+ T cells are also present in teleost fish. Here we review the literature that reported the use of antibodies against CD4 in a few teleost fish species and transcription profiling of Th cell-relevant genes in the context of viral infections and virus-relevant immunomodulation. Studies reveal massive CD4+ T cell proliferation and expression of key cytokines, transcription factors, and effector molecules that evoke mammalian Th cell responses. We also discuss gaps in the current understanding and evaluation of teleost CD4+ T cell responses and how development and application of novel tools and approaches to interrogate such responses could bridge these gaps. A greater understanding of fish Th cell responses will further illuminate the evolution of vertebrate adaptive immunity, inform strategies to address viral infections in aquaculture, and could further foster fish as model organisms.

Flow cytometric analysis of lymphocyte subset kinetics in Bali cattle experimentally infected with Jembrana disease virus

Jembrana disease virus (JDV) is an unusual bovine lentivirus that causes an acute and sometimes fatal disease after a short incubation period in Bali cattle (Bos javanicus). The pathological changes occur primarily in lymphoid tissues, which feature proliferating lymphoblastoid-like cells predominantly throughout parafollicular (T-cell) areas, and atrophy of follicles (B-cell) areas. Five Bali cattle were experimentally infected with JDV and all developed typical clinical signs of Jembrana disease characterised by a transient febrile response, enlargement of superficial lymph nodes and a significant leukopenia. Flow cytometric analysis of PBMC during the acute (febrile) disease phase showed that the reduced number of lymphocytes was due to a significant decrease in both the proportion and absolute numbers of CD4(+) T cells, but not CD8(+) T-cells or CD21(+) B-cells. At the end of the febrile phase, total numbers of both CD8(+) T-cells and CD21(+) B-cells increased significantly, while CD4(+) T-cell numbers remained below normal values, resulting in a significantly reduced CD4(+):CD8(+) ratio. We speculate that the persistent depletion of CD4(+) T cells following JDV infection, through lack of CD4(+) T cell help to B cells, may explain the lack of production of JDV-specific antibodies for several weeks after recovery despite an increase in CD21(+) B cell numbers. Further, our previous data showing that IgG(+) plasma cells are targets for JDV infection, correlated with our current data demonstrating an increase in CD8(+) T cell numbers, supports the suggestion that anti-viral cytotoxic T cell or other cell-mediated immune responses may be critical in the recovery process, although this remains to be formally demonstrated for JDV.

Early detection of dominant Env-specific and subdominant Gag-specific CD8+ lymphocytes in equine infectious anemia virus-infected horses using major histocompatibility complex class I/peptide tetrameric complexes

Cytotoxic T lymphocytes (CTL) are critical for control of lentiviruses, including equine infectious anemia virus (EIAV). Measurement of equine CTL responses has relied on chromium-release assays, which do not allow accurate quantitation. Recently, the equine MHC class I molecule 7-6, associated with the ELA-A1 haplotype, was shown to present both the Gag-GW12 and Env-RW12 EIAV CTL epitopes. In this study, 7-6/Gag-GW12 and 7-6/Env-RW12 MHC class I/peptide tetrameric complexes were constructed and used to analyze Gag-GW12- and Env-RW12-specific CTL responses in two EIAV-infected horses (A2164 and A2171). Gag-GW12 and Env-RW12 tetramer-positive CD8+ cells were identified in nonstimulated peripheral blood mononuclear cells as early as 14 days post-EIAV inoculation, and frequencies of tetramer-positive cells ranged from 0.4% to 6.7% of nonstimulated peripheral blood CD8+ cells during the 127-day study period. Although both horses terminated the initial viremic peak, only horse A2171 effectively controlled viral load. Neutralizing antibody was present during the initial control of viral load in both horses, but the ability to maintain control correlated with Gag-GW12-specific CD8+ cells in A2171. Despite Env-RW12 dominance, Env-RW12 escape viral variants were identified in both horses and there was no correlation between Env-RW12-specific CD8+ cells and control of viral load. Although Gag-GW12 CTL escape did not occur, a Gag-GW12 epitope variant arose in A2164 that was recognized less efficiently than the original epitope. These data indicate that tetramers are useful for identification and quantitation of CTL responses in horses, and suggest that the observed control of EIAV replication and clinical disease was associated with sustained CTL recognition of Gag-specific epitopes.