TREM2 and neoplasm: In addition, tumor-bearing SAMs displayed a high expression of complement C1q A chain and B chain (C1qa and C1qb) and triggering receptor expressed on myeloid cells 2 (Trem2), and a low expression of the major histocompatibility complexes (Cd74, H2-D1, H2-Aa, and H2-Eb1) compared with control SAMs (Fig 3A and B).