FOS and infection: In addition, the lymphocytes in 21-day infection also upregulated several chemokine receptors (e.g. CXCR5, CCR6, and CCR7), cytokines (e.g. IL23A), and transcription factors related to immune activation (e.g. FOS, FOSB, and NFKB1) compared to 12-days infection, suggesting an enhanced activation state of those cells.