title: Specific detection of antigen-binding cells by localized growth of bacteria.
abstract: A new method for the enumeration of lymphoid cells with specific surface-receptors for antigen is described, based on the use of beta-D-galactosidase (EC 3.2.1.23), either directly as an antigen or as a conjugated antigen. Binding of beta-D-galactosidase is revealed by its activity in releasing riboflavin from a synthetic substrate, riboflavin-beta-D-galactopyranoside. The riboflavin, inactive as a vitamin in the galactosidic form, becomes active when released by the enzyme, and can be detected by bioassay. Hence, lymphoid cells with receptors for beta-D-galactosidase on their surface can be detected after they have been exposed to the enzyme, washed, and then plated in agar containing riboflavin-beta-D-galactopyranoside, streptomycin, riboflavin-deficient medium, and a streptomycin-resistant strain of Streptococcus faecalis that requires riboflavin. Release of riboflavin is signalled by the growth of characteristic bacterial colonies over the cell that bound beta-D-galactosidase.
mesh_terms: D000818:Animals; D000937:Antigen-Antibody Reactions; D001665:Binding Sites; D001681:Biological Assay; D013293:Enterococcus faecalis / Q000254:growth & development* / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005696:Galactosidases / Q000032:analysis; D007114:Immunization; D008214:Lymphocytes / Q000276:immunology*; D008297:Male; D051379:Mice; D011714:Pyrans / Q000378:metabolism; D012256:Riboflavin / Q000032:analysis / Q000378:metabolism; D013154:Spleen / Q000166:cytology
chemical_list: D011714:Pyrans; D005696:Galactosidases; D012256:Riboflavin; D005690:Galactose