Intracellular concentrations of Ca(2+) modulate the strength of signal and alter the outcomes of cytotoxic T-lymphocyte antigen-4 (CD152)-CD80/CD86 interactions in CD4(+) T lymphocytes.
The costimulatory receptors CD28 and cytotoxic T-lymphocyte antigen (CTLA)-4 and their ligands, CD80 and CD86, are expressed on T lymphocytes; however, their functional roles during T cell-T cell interactions are not well known. The consequences of blocking CTLA-4-CD80/CD86 interactions on purified mouse CD4(+) T cells were studied in the context of the strength of signal (SOS). CD4(+) T cells were activated with phorbol 12-myristate 13-acetate (PMA) and different concentrations of a Ca(2+) ionophore, Ionomycin (I), or a sarcoplasmic Ca(2+) ATPase inhibitor, Thapsigargin (TG). Increasing concentrations of I or TG increased the amount of interleukin (IL)-2, reflecting the conversion of a low to a high SOS. During activation with PMA and low amounts of I, intracellular concentrations of calcium ([Ca(2+)](i)) were greatly reduced upon CTLA-4-CD80/CD86 blockade. Further experiments demonstrated that CTLA-4-CD80/CD86 interactions reduced cell cycling upon activation with PMA and high amounts of I or TG (high SOS) but the opposite occurred with PMA and low amounts of I or TG (low SOS). These results were confirmed by surface T-cell receptor (TCR)-CD3 signalling using a low SOS, for example soluble anti-CD3, or a high SOS, for example plate-bound anti-CD3. Also, CTLA-4-CD80/CD86 interactions enhanced the generation of reactive oxygen species (ROS). Studies with catalase revealed that H(2)O(2) was required for IL-2 production and cell cycle progression during activation with a low SOS. However, the high amounts of ROS produced during activation with a high SOS reduced cell cycle progression. Taken together, these results indicate that [Ca(2+)](i) and ROS play important roles in the modulation of T-cell responses by CTLA-4-CD80/CD86 interactions.
Ahmed
Asma
A
Department of Biochemistry, Indian Institute of Science, Bangalore, India.
Mukherjee
Sambuddho
S
Nandi
Dipankar
D
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D018122:B7-1 Antigen / Q000378:metabolism; D051940:B7-2 Antigen / Q000378:metabolism; D017252:CD3 Complex / Q000276:immunology; D060908:CTLA-4 Antigen; D002118:Calcium / Q000276:immunology* / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D049109:Cell Proliferation; D002470:Cell Survival / Q000276:immunology; D002478:Cells, Cultured; D005260:Female; D015759:Ionomycin / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000276:immunology; D019284:Thapsigargin / Q000494:pharmacology
D015703:Antigens, CD; D018122:B7-1 Antigen; D051940:B7-2 Antigen; D017252:CD3 Complex; D060908:CTLA-4 Antigen; C497965:Cd86 protein, mouse; C556707:Ctla4 protein, mouse; D017382:Reactive Oxygen Species; D015759:Ionomycin; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium