The 24.5-kb Left Variable Region Is Not a Determinant for African Swine Fever Virus to Replicate in Primary Porcine Alveolar Macrophages

African swine fever (ASF) is a widespread hemorrhagic and highly contagious infectious disease caused by African swine fever virus (ASFV), currently threatening the pig industry worldwide. Here, we demonstrated that the cell-adapted strain ASFV-P121 with a 24.5-kb deletion in the left variable region (LVR) lost the ability to replicate in primary porcine alveolar macrophages (PAMs). To explore whether this deletion determines the inability of ASFV-P121 replication in PAMs, a mutant virus (ASFV-Delta LVR) with the same LVR deletion as ASFV-P121 was constructed based on the wild-type ASFV HLJ/18 (ASFV-WT). However, the growth titer of ASFV-Delta LVR only reduced 10-fold compared with ASFV-WT in PAMs. Furthermore, we found that the large deletion of the LVR does not affect the formation of virus factories and virion morphogenesis. These findings reveal important implications for analyzing the molecular mechanism of ASFV cell tropism change.