CD4- CD8- TCR alpha/beta+ suppressor T cells demonstrated in mice 1 day after thermal injury

Lymphocyte Immunosuppression and Dysfunction Contributing to Persistent Inflammation, Immunosuppression, and Catabolism Syndrome (PICS)

ABSTRACT

Persistent Inflammation, Immune Suppression, and Catabolism Syndrome (PICS) is a disease state affecting patients who have a prolonged recovery after the acute phase of a large inflammatory insult. Trauma and sepsis are two pathologies after which such an insult evolves. In this review, we will focus on the key clinical determinants of PICS: Immunosuppression and cellular dysfunction. Currently, relevant immunosuppressive functions have been attributed to both innate and adaptive immune cells. However, there are significant gaps in our knowledge, as for trauma and sepsis the immunosuppressive functions of these cells have mostly been described in acute phase of inflammation so far, and their clinical relevance for the development of prolonged immunosuppression is mostly unknown. It is suggested that the initial immune imbalance determines the development of PCIS. Additionally, it remains unclear what distinguishes the onset of immune dysfunction in trauma and sepsis and how this drives immunosuppression in these cells. In this review, we will discuss how regulatory T cells (Tregs), innate lymphoid cells, natural killer T cells (NKT cells), TCR-a CD4- CD8- double-negative T cells (DN T cells), and B cells can contribute to the development of post-traumatic and septic immunosuppression. Altogether, we seek to fill a gap in the understanding of the contribution of lymphocyte immunosuppression and dysfunction to the development of chronic immune disbalance. Further, we will provide an overview of promising diagnostic and therapeutic interventions, whose potential to overcome the detrimental immunosuppression after trauma and sepsis is currently being tested.

Contemporary Burn Survival

BACKGROUND

The standard of burn treatment today reflects major advances. We sought to quantitate the impact of these advances on burn survival via age-stratified mortality ratios compared with other reported mortality analyses in burns.

STUDY DESIGN

Age, percent of the total body surface area (TBSA) burned, presence of inhalation injury, length of stay, and survival status were recorded at admission and at discharge for all new burn admissions between 1989 and 2017. The expected mortality probability was calculated using historical multiple regression techniques and compared with observed data. We developed a prediction model for our observed data.

RESULTS

Between 1989 and 2017, there were 10,384 consecutive new burn admissions, with 355 mortalities (median age, 13 years; median percent TBSA burn, 11%). We saw a significant decrease in our observed mortality data compared to historical predictions (p < 0.0001), and a 2% reduction per year in mortality during the 3 decades. The prediction model of mortality for the data is as follows: Pr(dying) = ex/(1 + ex) where x = -6.44 - 0.12 age + 0.0042 age2 - 0.0000283 age3 + 0.0499 TBSA + 1.21 Inhalation Injury + 0.015 third degree TBSA.

CONCLUSIONS

The reduction in mortality over time may be attributed to successful changes in standard of care protocols in the burn center that improved the outlook for burned individuals, including protocols for management of inhalation injury, nutrition, resuscitation, and early excision and grafting.

The composition of T-cell subsets are altered in the burn wound early after injury

BACKGROUND

Burn-induced inflammation leads to impaired immune responses resulting in increased morbidity and mortality. T-cells are central in the immune response and circulating CD4 and CD8 T-cells have been used to evaluate immune status; however, the role of these T-cell subsets in the burn wound is unknown.

METHODS

Male C57BL/6 mice were subjected to a major 3rd degree scald burn or sham treatment. Twenty-four hours later, full thickness skin samples from sham mice and the burn wounds were collected and single cells were isolated and analyzed for αβ TCR, γδ TCR, CD3, CD4, CD8 and CD69 expressions by flow cytometry.

RESULTS

The burn wound contained significantly greater numbers of T-cells than skin from sham mice, due to a profound infiltration of αβ T-cells. These infiltrating αβ T-cells were primarily suppressor T-cells with a CD8+ or CD8-CD4- phenotype. The 15-fold increase in CD8+ αβ T-cells caused a decrease in the CD4:CD8 ratio from 0.7 in sham skin to 0.3 in the burn wound. In contrast, the majority of the γδ T-cells in sham skin were CD4-CD8-, which decreased 9-fold in the burn wound. CD69 expression was suppressed on burn wound αβ T-cells, but increased on γδ T-cells in the burn wound.

CONCLUSIONS

The infiltrating burn wound αβ T-cells likely act to quell inflammation. In contrast wound γδ T-cells were activated with elevated CD4 and CD69 expression. Thus, these two distinct T-cell subsets likely differentially regulate the burn wound inflammatory response.

The impact of muscle disuse on muscle atrophy in severely burned rats

BACKGROUND

Severe burn induces a sustained hypermetabolic response, which causes long-term loss of muscle mass and decrease in muscle strength. In this study, we sought to determine whether muscle disuse has additional impact on muscle atrophy after severe burn using a rat model combining severe cutaneous burn and hindlimb unloading.

METHODS

Forty Sprague-Dawley rats (≈ 300 g) were randomly assigned to sham ambulatory (S/A), sham hindlimb unloading (S/HLU), burn ambulatory (B/A), or burn hindlimb unloading (B/HLU) groups. Rats received a 40% total body surface (TBSA) full thickness scald burn, and rats with hindlimb unloading were placed in a tail traction system. At d 14, lean body mass (LBM) was determined using DEXA scan, followed by measurement of the isometric mechanical properties in the predominantly fast-twitch plantaris muscle (PL) and the predominantly slow-twitch soleus muscle (SL). Muscle weight (wt), protein wt, and wet/dry wt were determined.

RESULTS

At d 14, body weight had decreased significantly in all treatment groups; B/HLU resulted in significantly greater loss compared with the B/A, S/HLU, and S/A. The losses could be attributed to loss of LBM. PL muscle wt and Po were lowest in the B/HLU group (<0.05 versus S/A, S/HLU, or B/A). SL muscle wt and Po were significantly less in both S/HLU and B/HLU compared with that of S/A and B/A; no significant difference was found between S/HLU and B/HLU.

CONCLUSIONS

Cutaneous burn and hindlimb unloading have an additive effect on muscle atrophy, characterized by loss of muscle mass and decrease in muscle strength in both fast (PL) and slow (SL) twitch muscles. Of the two, disuse appeared to be the dominant factor for continuous muscle wasting after acute burn in this model.

Muscle contractile properties in severely burned rats

Burn induces a sustained catabolic response which causes massive loss of muscle mass after injury. A better understanding of the dynamics of muscle wasting and its impact on muscle function is necessary for the development of effective treatments. Male Sprague-Dawley rats underwent either a 40% total body surface area (TBSA) scald burn or sham burn, and were further assigned to subgroups at four time points after injury (days 3, 7, 14 and 21). In situ isometric contractile properties were measured including twitch tension (Pt), tetanic tension (Po) and fatigue properties. Body weight decreased in burn and sham groups through day 3, however, body weight in the sham groups recovered and increased over time compared to burned groups, which progressively decreased until day 21 after injury. Significant differences in muscle wet weight and protein weight were found between sham and burn. Significant differences in muscle contractile properties were found at day 14 with lower absolute Po as well as specific Po in burned rats compared to sham. After burn, the muscle twitch tension was significantly higher than the sham at day 21. No significant difference in fatigue properties was found between the groups. This study demonstrates dynamics of muscle atrophy and muscle contractile properties after severe burn; this understanding will aid in the development of approaches designed to reduce the rate and extent of burn induced muscle loss and function.

Changes in Cytokine Levels and CD4+/CD8+ T Cells Ratio in Draining Lymph Node of Burn Wound

The aim of this study was to determine the changes of cytokine levels in draining lymph fluid and the changes of CD4+/CD8+ T-cells ratio in draining lymph node of burn wound. Male Wistar rats were subjected to unilateral hind limb burn (burn limbs group) and contralateral hind limb without burn (control limbs group). On hours 6, 24, and 72 after burn, rats were killed; lymph fluid in the efferent lymph trunk of the common iliac lymph nodes (CILN) were collected; and lymph fluid Interferon-gamma (IFN-gamma), interleukin-4 (IL-4) and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured by enzyme-linked immunosorbent assay. The CD4+/CD8+ T cells ratio of CILN was submitted to flow cytometry. The results showed TNF-alpha concentrations were significantly greater in the burn limbs group when compared with the control limbs group (P < .05). The IFN-gamma/IL-4 ratio was significantly lower (P < .05). The CD4+/CD8+ T-cell ratio was significantly lower on postburn hours 72 (P < .05). This study provides evidence that the burn wound can increase TNF-alpha levels and decrease IFN-gamma/ IL-4 ratio in the draining lymph fluid and decrease CD4+/CD8+ T cells ratio in the draining lymph node.

Double-negative regulatory T cells: non-conventional regulators

The crucial role of regulatory T (Treg) cells in self-tolerance and downregulating immune responses has been clearly established. Numerous different Treg subsets have been identified that possess distinct phenotypes and functions in various disease models. Among these subsets, alphabeta-TCR+CD3+CD4-CD8- double-negative (DN) Treg cells have been shown to be able to inhibit a variety of immune responses in part via direct killing of effector T cells in an antigenspecific manner in both mice and humans. This was shown to occur at least partially by acquisition of MHC-peptide complexes from antigen-presenting cells (APCs) and subsequent Fas/Fas-ligand interactions. In addition, DN Treg cells have been shown to express several molecules uncommon to other Treg cell subsets, such as IFN-gamma, TNF-alpha, Ly6A, FcRgamma, and CXCR5, which may contribute to their unique regulatory ability. Understanding the development and regulatory functions of DN Treg cells may elucidate the etiology for loss of self-tolerance and serve as a therapeutic modality for various diseases. This review will summarize the characteristics, developmental pathways, and mechanisms of action of DN Treg cells, as well as their role in transplant tolerance, autoimmunity, and anticancer immunity.

Insulin-like growth factor-I/insulin-like growth factor binding protein-3 alters lymphocyte responsiveness following severe burn

PURPOSE

Following severe burn, patients are immunocompromised, making them at increased risk for infection. Exogenous growth hormone has been shown to partially restore immune function. Herein, we investigated Th1/Th2 cytokine profiles and cellular proliferation in isolated mononuclear cells after treatment with exogenous insulin-like growth factor-I (IGF-I), the indirect mediator of many growth hormone effects, in severely burned patients.

METHODS

Eight children and 2 adults with >20% total body surface area burns were prospectively randomized to receive either placebo or 4 mg/kg rhIGF-I/IGFBP-3 for one-week intervals (2 groups), with another group receiving placebo for both cycles. Normal children were examined for comparison. Isolated whole blood lymphocyte production of Th1 (IL-2, IFN-gamma) and Th2 (IL-4, IL-10) cytokines, and proliferative responses to specific T-cell mitogens were measured.

RESULTS

Depressed Th1 and exaggerated Th2 cytokine responses were seen in all burned subjects compared to non-burned controls (P < 0.05). IL-2 and IFN-gamma production increased in patients treated with IGF-I/IGFBP-3 (P < 0.05). IL-4 production significantly decreased, while IL-10 levels did not change. Cytokine production did not change in those receiving two courses of placebo. Proliferative responses of isolated mononuclear cells to IL-2 as a Th1 specific mitogen increased with IGF-I/IGFBP-3 treatment (P < 0.05).

CONCLUSIONS

Following severe burn, a shift occurs toward a predominant Th2 phenotype. Exogenous IGF-I/IGFBP-3 treatment partially reverses this response.

CD8(+) T cells express a T-helper 1--like phenotype after burn injury

BACKGROUND

Previous studies suggest that CD8(+) T cells are immunosuppressive after burn injury, but recent reports indicate that CD8(+) T cells have several functions similar to CD4(+) T cells, including the secretion of cytokines. This study uses HY male antigen in transgenic HY female mice to determine the antigen-specific response of activated CD8(+) T cells after burn injury.

METHODS

HY TCR transgenic female mice underwent burn or sham injury. Seventy-two hours after the burn, splenocytes were stimulated with 20 micromol/L HY peptide for 16, 48, and 64 hours; cellular proliferation, intracellular interferon-gamma and interleukin-2, and apoptosis were measured.

RESULTS

Burn injury significantly impaired proliferation to HY antigen (P < or =.05). Activated CD8(+) T cells from burned mice showed increased intracellular interferon-gamma and interleukin-2 16 hours after stimulation compared with sham (P < or =.05) and at no time was less than control mice. The percent of CD8(+) T cells decreased with the time of stimulation but was not due to apoptosis by Annexin V staining.

CONCLUSIONS

Activated CD8(+) T cells express a T(h1)-like phenotype after burn injury. This provides evidence that CD8(+) T cells are not simply suppressive and that is consistent with data that CD4(+) T cells are primed for a T(h1) response after burn injury.

The regulation of burn-associated infections with herpes simplex virus type 1 or Candida albicans by a non-toxic aconitine-hydrolysate, benzoylmesaconine. Part 1: Antiviral and anti-fungal activities in thermally injured mice

As compared with normal unburned mice, thermally injured mice have been shown to be 50-100 times more susceptible to HSV type 1 (HSV-1) or Candida albicans infection. Benzoylmesaconine (BEN) improved the resistance of thermally injured mice against infection with HSV-1 or C. albicans to the level observed in normal mice. Mortality rates of normal mice exposed to lethal amounts of these pathogens were not affected by the BEN treatment, while significant survival effects were produced in these mice after treatment with acyclovir (against HSV-1) or amphotericin B (against C. albicans). Benzoylmesaconine did not inhibit the growth of these pathogens in vitro and did not directly reduce the viability of the pathogens. However, burned mice inoculated with CD4+ T cells from BEN-treated mice resisted infections from these pathogens. These results suggested that, through the generation of CD4+ T cells, BEN recovered the impaired resistance of thermally injured mice to infection by HSV-1 or C. albicans.

The regulation of burn-associated infections with herpes simplex virus type 1 or Candida albicans by a non-toxic aconitine-hydrolysate, benzoylmesaconine. Part 2: Mechanism of the antiviral action

In the accompanying paper, the resistance to infections with HSV type 1 (HSV-1) and Candida albicans was improved in thermally injured mice treated with benzoylmesaconine (BEN), an aconitine-hydrolysate isolated from heated Aconiti tuber, or inoculated with splenic CD4+ T cells from BEN-treated mice (BEN T cells). In this paper, therefore, the antiviral mechanism of BEN T cells (or BEN) on the improved resistance of burned mice to the HSV-1 infection was studied. Burn-associated CD + CD11b+ TCRgamma/delta+ type-2 T cells have been shown to be a key on the increased susceptibility of thermally injured mice to infection with HSV-1 or C. albicans. The susceptibility of T6S-mice, mice inoculated with 1 x 10(6) cells/mouse of T6S cells (a clone of burn-associated type-2 T cells), to HSV-1 infection was similar to that of thermally injured mice. The adoptive transfer of BEN T cells to T6S-mice restores their impaired resistance to HSV-1 infection. The type-2 cytokine levels in sera of T6S-mice were decreased after inoculation of BEN T cells. BEN T cells inhibited the type-2 cytokine production by T6S cells when they were cocultured in vitro. BEN T cells, characterized as CD4+ CD28+ TCRalpha/beta+ Vicia villosa (VV) lectin-adherent T cells, showed non-specific ability to inhibit the cytokine production by various type-2 T cells. From the results of the cytokine-producing profile, BEN T cells were shown to be a different subset of CD4+ T cells from Th1 and Th2 cells, although these three CD4+ T cells had similar properties phenotypically. BEN T cells were induced in normal mice 1-4 days after the oral treatment of BEN (1 microg/kg or more). These results suggest that, through the induction of antagonistic CD4+ T cells against burn-associated type-2 T cells, BEN may improve the resistance of T6S-mice (or thermally injured mice) to the infection of HSV-1.