TY - JOUR
T1 - T cell resistance to activation by dendritic cells requires long-term culture in simulated microgravity
AU - Bradley, Jillian H.
AU - Stein, Rachel
AU - Randolph, Brad
AU - Molina, Emily
AU - Arnold, Jennifer P.
AU - Gregg, Randal K.
N1 - Funding Information:
We would like to thank Nichole Tackett for her technical assistance. Research reported in this publication was supported by funds provided through the Division of Biomedical Sciences, Edward Via College of Osteopathic Medicine Carolinas Campus.
Publisher Copyright:
© 2017 The Committee on Space Research (COSPAR)
PY - 2017/11
Y1 - 2017/11
N2 - Immune impairment mediated by microgravity threatens the success of space exploration requiring long-duration spaceflight. The cells of most concern, T lymphocytes, coordinate the host response against microbial and cancerous challenges leading to elimination and long-term protection. T cells are activated upon recognition of specific microbial peptides bound on the surface of antigen presenting cells, such as dendritic cells (DC). Subsequently, this engagement results in T cell proliferation and differentiation into effector T cells driven by autocrine interleukin-2 (IL-2) and other cytokines. Finally, the effector T cells acquire the weaponry needed to destroy microbial invaders and tumors. Studies conducted on T cells during spaceflight, or using Earth-based culture systems, have shown reduced production of cytokines, proliferation and effector functions as compared to controls. This may account for the cases of viral reactivation events and opportunistic infections associated with astronauts of numerous missions. This work has largely been based upon the outcome of T cell activation by stimulatory factors that target select T cell signaling pathways rather than the complex, signaling events related to the natural process of antigen presentation by DC. This study tested the response of an ovalbumin peptide-specific T cell line, OT-II TCH, to activation by DC when the T cells were cultured 24–120 h in a simulated microgravity (SMG) environment generated by a rotary cell culture system. Following 72 h culture of T cells in SMG (SMG-T) or control static (Static-T) conditions, IL-2 production by the T cells was reduced in SMG-T cells compared to Static-T cells upon stimulation by phorbol 12-myristate 13-acetate (PMA) and ionomycin. However, when the SMG-T cells were stimulated with DC and peptide, IL-2 was significantly increased compared to Static-T cells. Such enhanced IL-2 production by SMG-T cells peaked at 72 h SMG culture time and decreased thereafter. When activation of SMG-T cells occurred in SMG, the T cells produced less IL-2 than control T cell cultures upon incubation with PMA and ionomycin. Short-term (24 h) SMG culture and activation of T cells by DC resulted in enhanced IL-2 production compared to Static-T cells, however, when culture was extended to 120 h, SMG-T cells secreted significantly less IL-2 than Static-T cells. SMG-T cell IL-2 doubled upon stimulation of the DC prior to addition to the T cell culture but remained less than control. SMG-T cell resistance to activation appeared comparable to the phenomenon of T cell exhaustion observed in patients with chronic diseases or persistent tumors. That is, long-term culture of T cells in SMG resulted in increased expression of the inhibitory receptor, CTLA-4. Blockade of CTLA-4 interaction with DC ligands resulted in improved T cell IL-2 production. Overall, this is the first study to determine the efficacy of DC in activating peptide-specific T cells. Furthermore, the findings suggests that countermeasures to restore T cell responsiveness in astronauts during long-term spaceflight or those living in microgravity environments should target possible inhibitory pathways that arise on activated T cells following stimulation.
AB - Immune impairment mediated by microgravity threatens the success of space exploration requiring long-duration spaceflight. The cells of most concern, T lymphocytes, coordinate the host response against microbial and cancerous challenges leading to elimination and long-term protection. T cells are activated upon recognition of specific microbial peptides bound on the surface of antigen presenting cells, such as dendritic cells (DC). Subsequently, this engagement results in T cell proliferation and differentiation into effector T cells driven by autocrine interleukin-2 (IL-2) and other cytokines. Finally, the effector T cells acquire the weaponry needed to destroy microbial invaders and tumors. Studies conducted on T cells during spaceflight, or using Earth-based culture systems, have shown reduced production of cytokines, proliferation and effector functions as compared to controls. This may account for the cases of viral reactivation events and opportunistic infections associated with astronauts of numerous missions. This work has largely been based upon the outcome of T cell activation by stimulatory factors that target select T cell signaling pathways rather than the complex, signaling events related to the natural process of antigen presentation by DC. This study tested the response of an ovalbumin peptide-specific T cell line, OT-II TCH, to activation by DC when the T cells were cultured 24–120 h in a simulated microgravity (SMG) environment generated by a rotary cell culture system. Following 72 h culture of T cells in SMG (SMG-T) or control static (Static-T) conditions, IL-2 production by the T cells was reduced in SMG-T cells compared to Static-T cells upon stimulation by phorbol 12-myristate 13-acetate (PMA) and ionomycin. However, when the SMG-T cells were stimulated with DC and peptide, IL-2 was significantly increased compared to Static-T cells. Such enhanced IL-2 production by SMG-T cells peaked at 72 h SMG culture time and decreased thereafter. When activation of SMG-T cells occurred in SMG, the T cells produced less IL-2 than control T cell cultures upon incubation with PMA and ionomycin. Short-term (24 h) SMG culture and activation of T cells by DC resulted in enhanced IL-2 production compared to Static-T cells, however, when culture was extended to 120 h, SMG-T cells secreted significantly less IL-2 than Static-T cells. SMG-T cell IL-2 doubled upon stimulation of the DC prior to addition to the T cell culture but remained less than control. SMG-T cell resistance to activation appeared comparable to the phenomenon of T cell exhaustion observed in patients with chronic diseases or persistent tumors. That is, long-term culture of T cells in SMG resulted in increased expression of the inhibitory receptor, CTLA-4. Blockade of CTLA-4 interaction with DC ligands resulted in improved T cell IL-2 production. Overall, this is the first study to determine the efficacy of DC in activating peptide-specific T cells. Furthermore, the findings suggests that countermeasures to restore T cell responsiveness in astronauts during long-term spaceflight or those living in microgravity environments should target possible inhibitory pathways that arise on activated T cells following stimulation.
KW - Antigen presentation
KW - Countermeasures
KW - Interleukin-2
KW - Rotary cell culture system
KW - Simulated microgravity
KW - T cells
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U2 - 10.1016/j.lssr.2017.08.002
DO - 10.1016/j.lssr.2017.08.002
M3 - Article
C2 - 29198314
AN - SCOPUS:85044668700
SN - 2214-5524
VL - 15
SP - 55
EP - 61
JO - Life Sciences in Space Research
JF - Life Sciences in Space Research
ER -