minimum number of aa residues needed to form an linear B-cell epitope

[milen]

Greetings,

If it is true that antibodies "recognize" surfaces, then
what would be minimum number of aa residues needed to form 
an effective linear B-cell epitope - 1 or 2 or 3 or 4 or 5 or.. ?.

All the best, 
Milen
Milen Vassilev MD
Clinic of Gastroenterology
Univ. Hosp. "St Ivan Rilskii"
15, D.Nestorov str.,
Sofia -1431
Bulgaria
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e-mail: milen at sun@medun.acad.bg(office)
        mvasilev at sf.cit.bg(private)