No abstract

The present study shows that reimmunization with tetanus toxoid (tet) caused a transient increase of the human blood plasma cell (PC) pool, detectable from 6th to 15th day postboost, as well as the temporal alteration of several PC features. Labeling of specific PC with FITC-tet C fragment (tetC) allowed kinetics analysis of the tetC+ and tetC− PC, and revealed remarkable differences between them: 1) the kinetics of tetC+ PC occurrence was exponential, and most of them appeared in a narrow time frame (5th to 8th day postboost), whereas the tetC− PC increase was lower (three to five times) and more prolonged (4th to 15th day postboost). 2) The tetC+ PC subset contained a fraction of cycling cells, expressed high levels of DR, CD138, and CD126, and responded to IL-6 by improving their survival and Ig secretion; in contrast, the tetC− PC showed higher CXCR4 and lower DR and CD138, did not respond to IL-6, and contained a fraction of apoptotic cells. 3) Sequential phenotypic analysis revealed maturational changes within the tetC+, but not tetC−, PC subset; sequencing of tetC+ PC IgVH genes showed clear features of Ag selection. 4) The tetC+ PC expressed several times more positive regulatory domain I- binding factor 1/B lymphocyte-induced maturation protein 1 transcription factor than the tetC− PC. 5) The tetC− PC and bone marrow resident PC similarly expressed low DR and high CXCR4, but differed in that the latter exhibited higher levels of CD31, CD138, and positive regulatory domain I- binding factor 1/B lymphocyte-induced maturation protein 1. These findings support the view that tetC+ PC contain bone marrow PC precursors, and tetC− PC probably belong to a removable compartment of aged PC.

Dense granules, a type of platelet secretory organelle, are known to accumulate high concentrations of small molecules such as calcium, adenine nucleotides, serotonin, pyrophosphate, and polyphosphate. Protein composition of these granules has been obscure, however. In this paper, we use proteomics techniques to describe, for the first time, the soluble protein composition of platelet dense granules. We have isolated highly enriched human platelet dense granule fractions that have been analyzed using two proteomics methods. Using this approach, we have identified 40 proteins, and most of them, such as actin-associated proteins, glycolytic enzymes, and regulatory proteins, have not previously been related to the organelle. We have focused our efforts on studying 14-3-3zeta, a member of a conserved family of proteins that interact with hundreds of different proteins. We have demonstrated that 14-3-3zeta is localized mostly on dense granules and that it is secreted after platelet activation. As some proteins secreted from activated platelets could promote the development of atherosclerosis and thrombosis, we have studied the expression of 14-3-3zeta in sections of human abdominal aorta of patients with aneurysm, identifying it at the atherosclerotic plaques. Together, our results reveal new details of the composition of the platelet dense granule and suggest an extracellular function for 14-3-3zeta associated with atherosclerosis.