Stressed-out B cells? Plasma-cell differentiation and the unfolded protein response.

Plasma cells operate as factories where large quantities of Ig heavy and light chains are made and assembled into functional antibodies. The finished products are shipped out with impressive efficiency. A major component of the machinery necessary for high-rate antibody secretion is an elaborate network of endoplasmic reticulum (ER), the site of antibody biosynthesis. Recent discoveries have provided insights into how this expansive secretory machinery is built, equipped and maintained. The unfolded protein response (UPR) pathway, a stress-induced signaling cascade emanating from the ER, regulates the expression and activity of X-box binding protein 1, a transcription factor required for plasma-cell development. The UPR pathway therefore senses conditions in the ER--the very compartment where antibodies are formed--and directs events required for humoral immunity.