A protective human monoclonal IgA antibody produced in vitro: Anti‐pneumococcal antibody engendered by Epstein‐Barr virus‐immortalized cell line

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Abstract
Human lymphocytes that produce anti-pneumococcal antibodies were separated and immortalized by Epstein-Barr virus and then cloned. One clone (NAD-Sel) produces an IgA, x antibody which is specific for the polysaccharides of type 8 pneumococcus, while not reactive with any of the polysaccharides derived from 24 other pneumococcal strains. The antibody, which is present in the cell supernatant as monomer and polymer, binds to protein A and does not fix complement. When incubated in vitro with type 8 pneumococci, it induces direct killing and increases the opsonization of these bacteria by mouse macrophages.