James A. Lederer

OBJECTIVE: Patients with serious traumatic injury and major burns and an animal model of burn injury were studied to determine the effect of injury on the production of cytokines typical of the T helper-2 lymphocyte phenotype as opposed to the T helper-1 phenotype and on the production of interleukin-12. SUMMARY BACKGROUND DATA: Perturbations of natural and adoptive immunity are related to the increased susceptibility to infection manifested by seriously injured and burn patients. Earlier work has shown that impaired adoptive immunity after injury is characterized by diminished production of interleukin-2 (IL-2), a product of Th lymphocytes. Exposure of naive Th cells to certain antigens and cytokines causes conversion to either the Th-1 or the Th-2 phenotype. Th-1 cells produce IL-2 and interferon-gamma (IFN-tau) and initiate cellular immunity. Th-2 cells secrete interleukin-4 (IL-4) and interleukin-10 (IL-10) and stimulate production of certain antibodies. Conversion to the Th-1 phenotype is facilitated by IL-12, and conversion to the Th-2 phenotype is promoted by IL-4. The authors believed that serious injury might cause conversion of Th cells to the Th-2 as opposed to the Th-1 phenotype rather than generalized Th suppression. METHODS: The authors studied circulating peripheral blood mononuclear cells (PBMC) from 16 major burn and 8 trauma patients on 32 occasions early after injury and from 13 age- and sex-matched healthy individuals for cytokine production after phytohemagglutinin stimulation. Also studied was a mouse model of 20% burn injury known to mimic the immune abnormalities seen in humans with burns. Splenocytes from burn mice, 10 to 12 per group, were studied after activation by concanavalin A or by the bacterial antigen Staphylococcus aureus Cowan strain I for cytokine production and cytokine messenger RNA expression as determined by reverse transcriptase polymerase chain reaction. Burn mice were compared with sham-burn controls and attention was focused on day 10 after burn injury, a time when IL-2 production and resistance to infection are highly suppressed. Finally, burn and sham-burn animals, 20 per group, were treated in vivo with IL-12 (25 ng daily for 5 days) and observed for mortality after septic challenge (cecal ligation and puncture [CLP]) performed on day 10 after injury. RESULTS: Peripheral blood mononuclear cells from burn and trauma patients produced less IFN-tau, the index cytokine of Th-1 cells, than PBMCs from healthy individuals 1 to 14 days after burn injury (SE = 77.6 +/- 16 pg/mL patients vs. 141.3 +/- 35 pg/mL controls, p < 0.05). However, production of IL-4, the index cytokine of Th-2 cells, by patient PBMCs was increased (51.0 +/- 13.0 pg/mL patients vs. 26.9 +/- 2.5 controls, p < 0.05). Splenocytes from mice 10 days after burn injury, when compared with sham-burn controls, showed diminished production of IL-2 (1.04 +/- 0.91 units/mL burns vs. 5.8 +/- 0.55 units/mL controls, p < 0.05) and IFN-tau (1.05 +/- 0.7 units/mL burns vs. 12.0 +/- 8.9 units/mL controls, p < 0.05). However, burn splenocytes produced more IL-4 (2492 +/- 157.0 pg/mL burns vs. 672.0 +/- 22.7 pg/mL controls, p < 0.01) and IL-10 (695.2 +/- 20.8 pg/mL burns vs. 567.0 +/- 16.7 pg/mL controls, p < 0.05). Splenocyte production of IL-12 was also reduced after burn (0.20 +/- 0.035 units/mL) as compared with sham burn (0.46 +/- 0.08 units/mL, p < 0.05). The reduction in IL-2, IFN-tau, and IL-12 production by burn splenocytes was reflected by a tenfold decrease in expression of their respective cytokine mRNAs. In vivo IL-12 treatment of burn animals decreased mortality from CLP on day 10 after injury from 85% to 15% (sham-burn mortality after CLP, 15%, p < 0.05) and increased splenocyte IFN-tau production to supranormal levels. CONCLUSIONS: Serious injury induced diminished production of IL-1 2 and a shift to the Th-2 phenotype with increased production of IL-4 and IL-10, cytokines known to inhibit Th-1 function. The ability of exogenous IL-12 to restore Th-1 cytokine production and resistance to infection suggests a therapeutic role for IL-12 in the immune dysfunction seen after major injury.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by pathologic T cell-B cell interactions and autoantibody production. Defining the T cell populations that drive B cell responses in SLE may enable design of therapies that specifically target pathologic cell subsets. Here, we evaluated the phenotypes of CD4+ T cells in the circulation of 52 SLE patients drawn from multiple cohorts and identified a highly expanded PD-1hiCXCR5-CD4+ T cell population. Cytometric, transcriptomic, and functional assays demonstrated that PD-1hiCXCR5-CD4+ T cells from SLE patients are T peripheral helper (Tph) cells, a CXCR5- T cell population that stimulates B cell responses via IL-21. The frequency of Tph cells, but not T follicular helper (Tfh) cells, correlated with both clinical disease activity and the frequency of CD11c+ B cells in SLE patients. PD-1hiCD4+ T cells were found within lupus nephritis kidneys and correlated with B cell numbers in the kidney. Both IL-21 neutralization and CRISPR-mediated deletion of MAF abrogated the ability of Tph cells to induce memory B cell differentiation into plasmablasts in vitro. These findings identify Tph cells as a highly expanded T cell population in SLE and suggest a key role for Tph cells in stimulating pathologic B cell responses.

OBJECTIVE: Programmed cell death-1 (PD-1) is a member of the CD28 superfamily that delivers negative signals on interaction with its 2 ligands, PD-L1 and PD-L2. We studied the contribution of the PD-1 pathway to regulation of T cells that promote atherosclerotic lesion formation and inflammation. METHODS AND RESULTS: We show that compared with Ldlr-/- control mice, Pd1-/-Ldlr-/- mice developed larger lesions with more abundant CD4+ and CD8+ T cells and macrophages, accompanied by higher levels of serum tumor necrosis factor-α. Iliac lymph node T cells from Pd1-/-Ldlr-/- mice proliferated more to αCD3 or oxidized low-density lipoprotein stimulation compared with controls. CD8+ T cells from Pd1-/-Ldlr-/- mice displayed more cytotoxic activity compared with controls in vivo and in vitro. Administration of a blocking anti-PD-1 antibody increased lesional inflammation in hypercholesterolemic Ldlr-/- mice with more lesional T cells and more activated T cells in paraaortic lymph nodes. The changes in lesional T-cell content when PD-1 was absent or blocked were also observed in bone marrow chimeric Ldlr-/- mice lacking PD-L1 and PD-L2 on hematopoietic cells. CONCLUSIONS: PD-1 has an important role in downregulating proatherogenic T-cell responses, and blockade of this molecule for treatment of viral infections or cancer may increase risk of cardiovascular complications.