After the process of affinity maturation in germinal centers, plasma cells have an indeterminate lifespan, ranging from days to months. Recently they have been shown to reside for much longer periods in the bone marrow as "long-lived plasma cells" (LLPC). These LLPCs represent a majority of plasma cells in the bone marrow, and can survive more than 90 days without DNA synthesis. They secrete high levels of antibodies, ranging from hundreds to thousands of antibodies per second per cell. Unlike their precursors, they cannot switch antibody classes, cannot act as antigen-presenting cells because they no longer display MHC-II, and do not take up antigen because they no longer display significant quantities of immunoglobulin on the cell surface. However, continued exposure to antigen through those low levels of immunoglobulin is important, as it partly determines the cell's lifespan.