Ultrasound biomicroscopy: a powerful tool probing murine lymph node size in vivo.

Invasive cell-counting in lymph node (LN) is the current reference to assess LN changes due to inflammation, immunodeficiency and cancer in murine models. This work evaluates whether ultrasound biomicroscopy (UBM) can measure LN size alterations noninvasively for a large range of sizes (0.1 mm3 to 22 mm3). Correlation was assessed (rho = 0.91, p < 0.0001) between invasive cell count and LN volume estimated with UBM (24, 2 to 28-week-old, C57BL/6 mice; 13 same-strain, transgenic mice presenting LN hyperplasia). UBM LN modification screening was applied in a skin-graft rejection model and compared with cell-counting (15 mice). UBM LN-size follow-up with fine temporal sampling was demonstrated from 9 d of age (minimum area 0.13 mm2). Reliability (intraclass correlation coefficient [ICC] > 0.84) and variability of UBM evaluations compared favourably with invasive cell count. UBM provides a noninvasive alternative to cell-counting in mice for early detection and longitudinal screening of LN modifications. This can enable significant reduction in the number of mice and exploration of LNs that would be too small to dissect for cell count.