SIGLEC1 and infection: Interestingly, a single amino acid substitution (Ala to Tyr at position 1683) in the CT of CD169 resulted in the endocytosis of CD169-bound HIV-1 and the mutant CD169 was unable to support trans-infection of T cells, suggesting surface retention by CD169 is critical for HIV-1 to gain access to the trans-infection pathway.