Comparison of Calcitonin Gene-Related Peptide Release from Rat Lymphocytes and Dorsal Root Ganglia Neurons

Calcitonin gene-related peptide (CGRP), a neuropeptide contained in primary sensory neurons, has been demonstrated to be synthesized and released by rat lymphocytes in our previous studies. In this study, the release properties and molecular characteristics of CGRP such as immunoreactivity (CGRP-LI) from lymphocytes were compared with those from dorsal root ganglia (DRG) neurons by using CGRP-specific RIA, reverse-phase HPLC, and RT-PCR. Con A and IL-2 could trigger CGRP-LI release from lymphocytes in a time-dependent manner. After 3 days stimulation with 4 microg/ml Con A, the level of CGRP-LI released by lymphocytes was increased from 77.4 +/- 9.6 pg/10(8) cells to 191.1 +/- 13.6 pg/10(8) cells and increased further to 374.5 +/- 38.3 pg/10(8) cells after 5 days. Stimulation with 750 U/ml human IL-2 recombinant (rhIL-2) caused a significantly elevated CGRP-LI release from 75.4 +/- 6.5 pg/10(8) cells to 266.2 +/- 16.2 pg/10(8) cells after 3 days and to 469.1 +/- 43.2 pg/10(8) cells after 5 days. Con A and IL-2 also augmented CGRP mRNA expression in lymphocytes. In the tested period (1-5 days), Con A and rhIL-2 had no stimulating effect on CGRP release from DRG neurons. In contrast, a high concentration of potassium and LPS could induce an acute release of CGRP from DRG neurons, but not from lymphocytes. Lymphocyte-released CGRP-LI was shown to coelute with synthetic rat CGRP (rCGRP) and DRG neuron-released CGRP by reverse-phase HPLC. In addition, to displace (125)I-CGRP from CGRP antibody by lymphocyte-released CGRP-LI was similar to that by synthetic rCGRP. These data suggest that lymphocyte- and nerve-derived CGRP-LI are similar in terms of immunological characteristics, molecular size, and polarity. However, lymphocytes secrete CGRP-LI in response to different stimuli compared to nerve-derived CGRP.