Investigating the interaction forces between T cells and antigen-presenting cells using an optical trapping system

The interactions between T cells and antigen-presenting cells (APCs) are crucial in triggering a successful antigen-specific, adaptive immune response leading to protection against a particular pathogen or disease. At present very little is known about the magnitudes of the forces involved in these interactions. We present results showing for the first time that optical tweezers can be used to measure these cell-cell interaction forces. We were able to see a significant difference in the force distributions taken with and without antigen, as evidenced by a Mann-Whitney U-test. The T cells of interest were trapped directly and no exogenous beads were added to the sample. Interaction forces between T cells and APCs in the presence of specific antigen ranged from 0-6.5 pN, whereas, when the specific antigen was absent the interaction forces ranged from 0-1.5 pN. The accuracy of the system will be discussed in terms of how we tracked the position of the optically trapped cell and the methods we used to minimise cell roll.