Less is known about EAV, which has elements distinct from but closely related to those of the ALV family of endogenous retroviruses.
We recently reported negative PCR results for ALV and EAV sequences in peripheral blood lymphocytes from 33 measles, mumps, and rubella (MMR) vaccine recipients (7).
Aliquots of lysates from 150,000 peripheral blood lymphocytes from MMR vaccine recipients were amplified by PCR for ALV env and EAV env-like sequences by using primers ALVENVF2/ ALVENVR2 and EAVENVF10/EAVENVR10, respectively (7).
The primers used for the RT reaction were ALVENVR2 and EAVENVR10 for ALV and EAV, respectively.
All 100 peripheral blood lymphocyte samples were negative for both ALV and EAV DNA sequences by PCR analysis (Figure 2).
We sought evidence of persistent ALV and EAV infection in a large number of MMR vaccine recipients, and we were unable to find any evidence of ALV or EAV sequences in peripheral blood lymphocytes, despite the use of highly sensitive PCR assays.
Human serum can lyse ALV by complement activation (23); however, this protective mechanism has not been demonstrated for endogenous ALV and EAV particles.
The presence of defective ALV and EAV particles in vaccines may also explain the lack of transmission of these viruses to vaccine recipients, ev loci confer a variety of different phenotypes, including infectious or defective particles (9,10,18,24).
EAV may represent the predominant retroviral particles in MMR vaccines (6,7).