A key role for capsid in determining interferon induction in macrophages was identified by infection with HIV-1(M) chimeras bearing HIV-1(O) or HIV-2 capsid (CA), which could only replicate in MDM in the presence of IFNAR1-Ab (Fig. 4a), in common with wild type (WT) HIV-2/HIV-1(O)(Fig. 1a–c). Here, IFNAR1 is linked to infection.