Abstract
BackgroundT cell activation and immune synapse formation require the appropriate activation and clustering of the integrin, LFA-1. Previous work has reported that the calpain family of calcium-dependent proteases are important regulators of integrin activation and modulate T cell adhesion and migration. However, these studies have been limited by the use of calpain inhibitors, which have known off-target effects.Methodology/Principal FindingsHere, we used a LoxP/CRE system to specifically deplete calpain 4, a small regulatory calpain subunit required for expression and activity of ubiquitously expressed calpains 1 and 2, in CD4+ T cells. CD4+ and CD8+ T cells developed normally in Capn4F/F:CD4-CRE mice and had severely diminished expression of Calpain 1 and 2, diminished talin proteolysis and impaired casein degradation. Calpain 4-deficient T cells showed no difference in adhesion or migration on the LFA-1 ligand ICAM-1 compared to control T cells. Moreover, there was no impairment in conjugation between Capn4F/F:CD4-CRE T cells and antigen presenting cells, and the conjugates were still capable of polarizing LFA-1, PKC-theta and actin to the immune synapse. Furthermore, T cells from Capn4F/F:CD4-CRE mice showed normal proliferation in response to either anti-CD3/CD28 coated beads or cognate antigen-loaded splenocytes. Finally, there were no differences in the rates of apoptosis following extrinsic and intrinsic apoptotic stimuli.Conclusion/SignificanceOur findings demonstrate that calpain 4 is not necessary for LFA-1-mediated adhesion, conjugation or migration. These results challenge previous reports that implicate a central role for calpains in the regulation of T cell LFA-1 function.
Highlights
CD4+ T cells are important regulators of the adaptive immune response
In order to test the role of calpain 4 in T cells, floxed calpain 4 mice [15], with loxP sites flanking exons 9 and 11, were crossed with mice expressing CRE recombinase driven off the CD4 promoter
Using laser scanning confocal microscopy, we found no difference in polarization of LFA-1, actin or PKC-theta to the immune synapse between Capn4+/+:CD4-CRE and Capn4F/F:CD4-CRE and antigen loaded LB27.4 cells, suggesting that calpain is not required for immune synapse formation (Figure 3 C,D)
Summary
CD4+ T cells are important regulators of the adaptive immune response. Following T cell receptor (TCR) recognition of its cognate peptide-MHC complex and costimulation, signaling leads to prolonged T cell:APC interactions, described as an immune synapse, which culminates in T cell activation, proliferation and cytokine production [1]. Formation of the immune synapse requires the activity of the integrin LFA-1 (aLb2), and mice lacking LFA-1 exhibit impaired T cell proliferation and cytokine responses following antigen exposure in vivo [2]. Previous work has shown that the calpain family of cysteine proteases can cleave talin between the head and rod domain, thereby modulating the ability of talin to activate integrins [5]. Previous work has reported that the calpain family of calcium-dependent proteases are important regulators of integrin activation and modulate T cell adhesion and migration. These studies have been limited by the use of calpain inhibitors, which have known off-target effects
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
