Related Experiment Videos
Signal thresholds and modular synergy during expression of costimulatory molecules in B lymphocytes
K Natarajan1, N C Sahoo, K V Rao
1Immunology Group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India.
Insights
B cell activation involves distinct signaling pathways for CD80 and CD86. Intracellular calcium (Ca2+) drives CD86, while CD80 requires both calcium and CD54 signaling for optimal expression.
Area of Science:
- Immunology
- Cellular Signaling
Background:
- B cells play a crucial role in adaptive immunity.
- Surface molecules CD80 and CD86 are critical costimulatory ligands for T cell activation.
- Understanding the regulation of these molecules is key to controlling immune responses.
Purpose of the Study:
- To elucidate the intracellular pathways regulating CD80 and CD86 surface expression on B cells.
- To investigate the roles of B cell receptor (BCR) and CD54 signaling in costimulatory molecule upregulation.
- To identify the second messenger systems involved in these signaling pathways.
Main Methods:
- Analysis of intracellular signaling pathways in B cells.
- Stimulation of B cells using anti-IgM (BCR ligation) and anti-CD54 antibodies.
- Measurement of intracellular calcium (Ca2+) and cyclic AMP (cAMP) levels.
- Quantification of surface CD80 and CD86 expression.
Main Results:
- BCR cross-linking alone increased CD86 expression, dependent on intracellular Ca2+ influx.
- CD80 upregulation required co-stimulation via anti-IgM and anti-CD54.
- CD80 induction involved a synergistic interaction between Ca2+ and cAMP, mediated by CD54 signaling.
- Distinct signaling requirements and cross-talk explain variable costimulatory molecule expression.
Conclusions:
- Intracellular Ca2+ is a key mediator for CD86 expression.
- CD80 expression is tightly regulated by the convergence of BCR and CD54 signaling pathways.
- Synergistic signaling involving Ca2+ and cAMP overcomes concentration thresholds for second messenger recruitment, enabling CD80 upregulation.
Abstract:
We analyzed intracellular pathways modulating surface densities of CD80 and CD86 in B cells activated through ligation of the Ag receptor, and the adhesion molecule CD54. Whereas B cell Ag receptor (BCR) cross-linking alone stimulated increased expression of CD86, up-regulation of CD80 required dual stimulation with anti-IgM and anti-CD54. The principal downstream component contributed by BCR signaling, toward both CD80 and CD86 induction, was the elevated concentration of free cytoplasmic Ca(2+), recruited by way of capacitative influx. This alone was sufficient to generate an increase in CD86 levels. However, CD80 enhancement required the concerted action of both intracellular Ca(2+) concentration and CD54-initiated pathways. The nexus between anti-IgM and anti-CD54 stimulation, in the context of CD80 regulation, was identified to involve a self-propagating process of sequential synergy. The first step involved amplified accumulation of intracellular cAMP, as a result of cross-talk between BCR-mobilized Ca(2+) and CD54-derived signals. This then facilitated a second synergistic interaction between Ca(2+) and cAMP, culminating in CD80 expression. Our findings of distinct signal transducer requirements, with the added consequences of cross-talk, offers an explanation for variable modulation of costimulatory molecule expression in response to diverse physiological stimuli. Importantly, these results also reveal how concentration threshold barriers for recruitment of individual second messengers can be overcome by constructive convergence of signaling modules.