# Mature Human Bone Marrow Plasma Cells Secrete More IgG than Early-Minted Blood Antibody-Secreting Cells

## TL;DR

Mature bone marrow plasma cells secrete more IgG antibodies than younger blood cells, showing increased antibody production as they mature.

## Contribution

Demonstrates that mature bone marrow ASC secrete more IgG than early blood ASC using an in vitro BM mimetic system.

## Key findings

- Mature BM ASC secrete more IgG per cell than immature blood ASC.
- Blood ASC can mature into LLPC phenotypes in culture, increasing IgG secretion.
- ASC on day 7 secrete more IgG than day 0 input ASC, showing maturation effects.

## Abstract

Plasma cells are known antibody-secreting factories with immunoglobulin (Ig) transcripts that increase as the cell matures into a long-lived plasma cell (LLPC) in the bone marrow (BM). Whether the Ig secretion rates among human antibody-secreting cells (ASC) are homogeneous or BM LLPC are capable of secreting more antibodies per cell compared to early-minted blood ASC remain unclear. Here, we use bulk and single cell cultures in a novel in vitro BM mimetic survival system to measure the IgG secretion rates of human ASC. We find that the mature BM ASC produce more IgG molecules per cell compared to immature, early-minted blood ASC. Furthermore, these blood ASC can mature into LLPC phenotypes in culture, and we show that ASC on day 7 secrete more IgG per cell than the input ASC from day 0. Thus, as human ASC mature, they increase the number of Ig transcripts and result in higher Ig secretion. These results also demonstrate that the mature ASC in the BM have higher Ig secretion rates compared to early-minted blood ASC.