Lama, Jyoti

Abstract After activation, CD4+ T cells undergo metabolic modifications in order to orchestrate successful immune responses. In particular, naïve T cells shift to a more glycolysis-heavy metabolic program that produces the necessary metabolites for growth, division, and exertion of effector function. Histone Deacetylase 3 (HDAC3) has been shown to epigenetically regulate many T cell fate decisions and is also capable of post-translationally modifying non-histone proteins. Deletion of HDAC3 in mature CD4+ T cells using a distal Lck-Cre HDAC3 cKO mouse revealed a reduction in differentiated T-helper cell populations in vivo. In contrast, in vitro differentiation of HDAC3-deficient CD4+ T cells occurred normally, however, the numbers of T cells present within each culture was greatly diminished. CD3/CD28-stimulated HDAC3-deficient cells exhibited poor proliferation with decreased blastogenesis, decreased CD25 expression, and decreased IL-2 production. Signaling downstream of TCR is disrupted in the HDAC3-deficient T cells. HDAC3-deficient CD4+ T cells have an overabundance of Foxo1 protein, and diminished signaling downstream of mTOR, including reduced phosphorylation of Ribosomal Protein S6, and decreased expression of Egr2. Key transporters involved in cholesterol efflux, ABCA1 and ABCG1, were upregulated in HDAC3-deficient CD4+ T cells. Strikingly, the proliferation and blasting defects of HDAC3-deficient CD4+ T cells are restored with the addition of exogenous cholesterol, but the signaling defects remain. Thus, the failure of HDAC3-deficient CD4+ T cells to proliferate is due to alterations in cholesterol homeostasis.

Abstract Food allergy, such as peanut allergy can cause life-threatening anaphylaxis. While T follicular helper (Tfh) cells play a major role in production of allergen-specific IgE and IgG antibodies, the immunologic mechanisms that regulate the production of antibodies that mediate anaphylaxis are not well understood. While PD-1 is highly expressed on Tfh cells, our knowledge is limited regarding the role of the molecule in Tfh cells. Thus, the objective of this study was to investigate the roles of PD-1 in allergic immune responses using a mouse model of peanut allergy. Naïve wild-type mice were exposed to peanut flour intranasally (i.n.) and then challenged by intraperitoneal (i.p.) injection of peanut extract. The mice exposed i.n. to peanut flour produced peanut-specific IgE and IgG antibodies and developed anaphylaxis when challenged i.p. with peanut extract. PD-1 blockade with anti-PD-1 treatment Tfh and germinal center B cell numbers in mice exposed to peanut flour. Nonetheless, anti-PD-1 or anti-PD-L1 fully protected mice from anaphylaxis. Anti-PD-1 or genetic deficiency of PD-1 in CD4+ T cells reduced and increased levels of peanut-specific IgE and IgG, respectively. Anti-PD-1 promoted production of low-affinity IgE and IgG antibodies with no effect on high-affinity antibodies. By passive cutaneous anaphylaxis, peanut-specific antibodies generated in anti-PD1 treated mice failed to induce anaphylaxis, and plasma from these mice prevented anaphylaxis. Therefore, blockade of the PD-1 pathway is protective against allergic immune responses. The interaction between Tfh cells and B cells may play a pivotal role in controlling antibody quality and clinical manifestation of allergic diseases.

After antigenic activation, quiescent naive CD4 + T cells alter their metabolism to proliferate. This metabolic shift increases production of nucleotides, amino acids, fatty acids, and sterols. Here, we show that histone deacetylase 3 (HDAC3) is critical for activation of murine peripheral CD4 + T cells. HDAC3-deficient CD4 + T cells failed to proliferate and blast after in vitro TCR/CD28 stimulation. Upon T-cell activation, genes involved in cholesterol biosynthesis are upregulated while genes that promote cholesterol efflux are repressed. HDAC3-deficient CD4 + T cells had reduced levels of cellular cholesterol both before and after activation. HDAC3-deficient cells upregulate cholesterol synthesis appropriately after activation, but fail to repress cholesterol efflux; notably, they overexpress cholesterol efflux transporters ABCA1 and ABCG1. Repression of these genes is the primary function for HDAC3 in peripheral CD4 + T cells, as addition of exogenous cholesterol restored proliferative capacity. Collectively, these findings demonstrate HDAC3 is essential during CD4 + T-cell activation to repress cholesterol efflux.