ERVFRD-1 and COVID-19: According to a transcriptome analysis, the expression of HERV-FRD, HERV-H, HERV-W, HERV-L, HERV-I, HERV-K (HML-5), HERV-K (HML-3) and HERV-K (HML-1) is significantly upregulated in bronchoalveolar lavage fluid (BALF) of COVID-19 patients compared to that in BALF of healthy individuals but not in the peripheral blood monocytes (PBMCs) (Kitsou et al. 2021).