The 17A2 monoclonal antibody reacts with mouse CD3, a transmembrane cell-surface protein that belongs to the immunoglobulin superfamily. CD3 associates with TCR α/β or γ/δ chains to form the TCR complex. CD3 is expressed on T lymphocytes, NK-T cells, and to varying degrees on developing thymocytes. CD3 plays roles in TCR signaling, T lymphocyte activation, and antigen recognition. The 145-2C11 antibody has been shown to block the binding of the 17A2 antibody suggesting that the 17A2 antibody recognizes an epitope of the CD3ε chain. Treatment with the 17A2 antibody in vivo has been reported to partially deplete T lymphocytes and temporarily down-modulate CD3 expression on T cells.

INVIVOMAB ANTI-MOUSE CD3 (CLONE: 17A2)

Choi, Y. S., et al. (2015). “LEF-1 and TCF-1 orchestrate TFH differentiation by regulating differentiation circuits upstream of the transcriptional repressor Bcl6.” Nat Immunol 16(9): 980-990. PubMed

Follicular helper T cells (TFH cells) are specialized effector CD4(+) T cells that help B cells develop germinal centers (GCs) and memory. However, the transcription factors that regulate the differentiation of TFH cells remain incompletely understood. Here we report that selective loss of Lef1 or Tcf7 (which encode the transcription factor LEF-1 or TCF-1, respectively) resulted in TFH cell defects, while deletion of both Lef1 and Tcf7 severely impaired the differentiation of TFH cells and the formation of GCs. Forced expression of LEF-1 enhanced TFH differentiation. LEF-1 and TCF-1 coordinated such differentiation by two general mechanisms. First, they established the responsiveness of naive CD4(+) T cells to TFH cell signals. Second, they promoted early TFH differentiation via the multipronged approach of sustaining expression of the cytokine receptors IL-6Ralpha and gp130, enhancing expression of the costimulatory receptor ICOS and promoting expression of the transcriptional repressor Bcl6.

 

Nance, J. P., et al. (2015). “Bcl6 middle domain repressor function is required for T follicular helper cell differentiation and utilizes the corepressor MTA3.” Proc Natl Acad Sci U S A. pii: 201507312. PubMed

T follicular helper (Tfh) cells are essential providers of help to B cells. The transcription factor B-cell CLL/lymphoma 6 (Bcl6) is a lineage-defining regulator of Tfh cells and germinal center B cells. In B cells, Bcl6 has the potential to recruit distinct transcriptional corepressors through its BTB domain or its poorly characterized middle domain (also known as RDII), but in Tfh cells the roles of the Bcl6 middle domain have yet to be clarified. Mimicked acetylation of the Bcl6 middle domain (K379Q) in CD4 T cells results in significant reductions in Tfh differentiation in vivo. Blimp1 (Prdm1) is a potent inhibitor of Tfh cell differentiation. Although Bcl6 K379Q still bound to the Prdm1 cis-regulatory elements in Tfh cells, Prdm1 expression was derepressed. This was a result of the failure of Bcl6 K379Q to recruit metastasis-associated protein 3 (MTA3). The loss of Bcl6 function in Bcl6 K379Q-expressing CD4 T cells could be partially rescued by abrogating Prdm1 expression. In addition to Prdm1, we found that Bcl6 recruits MTA3 to multiple genes involved in Tfh cell biology, including genes important for cell migration, cell survival, and alternative differentiation pathways. Thus, Bcl6 middle domain mediated repression is a major mechanism of action by which Bcl6 controls CD4 T-cell fate and function.

 

Hu, S., et al. (2014). “Activated CD8+ T lymphocytes inhibit neural stem/progenitor cell proliferation: role of interferon-gamma.” PLoS One 9(8): e105219. PubMed

The ability of neural stem/progenitor cells (NSCs) to self-renew, migrate to damaged sites, and differentiate into neurons has renewed interest in using them in therapies for neurodegenerative disorders. Neurological diseases, including viral infections of the brain, are often accompanied by chronic inflammation, whose impact on NSC function remains unexplored. We have previously shown that chronic neuroinflammation, a hallmark of experimental herpes simplex encephalitis (HSE) in mice, is dominated by brain-infiltrating activated CD8 T-cells. In the present study, activated CD8 lymphocytes were found to suppress NSC proliferation profoundly. Luciferase positive (luc+) NSCs co-cultured with activated, MHC-matched, CD8+ lymphocytes (luc-) showed two- to five-fold lower luminescence than co-cultures with un-stimulated lymphocytes. On the other hand, similarly activated CD4+ lymphocytes did not suppress NSC growth. This differential lymphocyte effect on proliferation was confirmed by decreased BrdU uptake by NSC cultured with activated CD8 T-cells. Interestingly, neutralizing antibodies to interferon-gamma (IFN-gamma) reversed the impact of CD8 lymphocytes on NSCs. Antibodies specific to the IFN-gamma receptor-1 subunit complex abrogated the inhibitory effects of both CD8 lymphocytes and IFN-gamma, indicating that the inhibitory effect of these cells was mediated by IFN-gamma in a receptor-specific manner. In addition, activated CD8 lymphocytes decreased levels of nestin and Sox2 expression in NSCs while increasing GFAP expression, suggesting possible induction of an altered differentiation state. Furthermore, NSCs obtained from IFN-gamma receptor-1 knock-out embryos were refractory to the inhibitory effects of activated CD8+ T lymphocytes on cell proliferation and Sox2 expression. Taken together, the studies presented here demonstrate a role for activated CD8 T-cells in regulating NSC function mediated through the production of IFN-gamma. This cytokine may influence neuro-restorative processes and ultimately contribute to the long-term sequelae commonly seen following herpes encephalitis.

 

Choi, Y. S., et al. (2013). “Bcl6 expressing follicular helper CD4 T cells are fate committed early and have the capacity to form memory.” J Immunol 190(8): 4014-4026. PubMed

Follicular helper CD4 T (Tfh) cells are a distinct type of differentiated CD4 T cells uniquely specialized for B cell help. In this study, we examined Tfh cell fate commitment, including distinguishing features of Tfh versus Th1 proliferation and survival. Using cell transfer approaches at early time points after an acute viral infection, we demonstrate that early Tfh cells and Th1 cells are already strongly cell fate committed by day 3. Nevertheless, Tfh cell proliferation was tightly regulated in a TCR-dependent manner. The Tfh cells still depend on extrinsic cell fate cues from B cells in their physiological in vivo environment. Unexpectedly, we found that Tfh cells share a number of phenotypic parallels with memory precursor CD8 T cells, including selective upregulation of IL-7Ralpha and a collection of coregulated genes. As a consequence, the early Tfh cells can progress to robustly form memory cells. These data support the hypothesis that CD4 and CD8 T cells share core aspects of a memory cell precursor gene expression program involving Bcl6, and a strong relationship exists between Tfh cells and memory CD4 T cell development.