Extrafollicular plasmablast B cells play a key role in carrying retroviralinfection to peripheral organs

B cells can either differentiate in germinal centers or in extrafollicular compartments of secondary lymphoid organs. Here we show the migration prope rties of B cells after differentiation in murine peripheral lymph node infe cted with mouse mammary tumor virus. Naive B cells become activated, infect ed, and carry integrated retroviral DNA sequences. After production of a re troviral superantigen, the infected B cells receive cognate T cell help and differentiate along the two main differentiation pathways analogous to cla ssical Ag responses. The extrafollicular differentiation peaks on day 6 of mouse mammary tumor virus infection, and the follicular one becomes detecta ble after day 10. B cells participating in this immune response carry a ret roviral DNA marker that can be detected by using semiquantitative PCR. We d etermined the migration patterns of B cells having taken part in the T cell -B cell interaction from the draining lymph node to different tissues. Wave s of immigration and retention of infected cells in secondary lymphoid orga ns, mammary gland, salivary gland, skin, lung, and liver were observed corr elating with the two peaks of B cell differentiation in the draining lymph node. Other organs revealed immigration of infected cells at later time poi nts. The migration properties were correlated with a strong up-regulation o f alpha (4)beta (1) integrin expression. These results show the migration p roperties of B cells during an immune response and demonstrate that a large proportion of extrafolliculary differentiating plasmablasts can escape loc al cell death and carry the retroviral infection to peripheral organs.