Forty -one samples of anti-Pr cold agglutinins (CA) were studied. The titers ranged from 4 to 32,000. As is the case with cold agglutinins of other specificities, immunoglobulin class M and k-type light chains predominated with anti-Pr CA. On the other hand, the few IgM lambda, IgG, and IgA found were associated preferentially with anti-Pr specificity. All anti-Pr CA were inhibited by human red cell membrane sialoglycoproteins. On the basis of an increased inhibition by sialoglycoproteins after periodate oxidation and carbodiimide treatment, respectively, three anti- Pr2 and five anti-Pr3 were found. Among 24 anti-Pr1 CA subclassified on the basis of agglutination with dog red cells, six were anti- Pr1h , 16 were anti- Pr1d , and two did not fit into the subclassification. Similar to the anti- Pr1h , - Pr1d subclassification, anti-Pr3 CA could be subclassified into anti- Pr3h , - Pr3d . Three anti-Pra examples were found. None of the anti-Pr CA was inhibited by N-acetylneuraminic acid; some (5/35) were inhibited by sialyllactose, NeuAc alpha 2-3 2-6 Gal beta 1-4Glc, in high doses (5.0-20.0 mM).
Postinfection cold agglutinins (CAs) with anti-Sia-b1 (i.e., anti-Sialo-branched) specificity frequently occurring together with anti-I CAs recognize antigenic determinants that are present on Oh red cells and are partially destroyed by endo-beta-galactosidase on the red cell surface. They differ markedly from the monoclonal anti-Sia-b1 FI CA, which recognizes an epitope not expressed on Oh cells, and resistant to the enzyme. On the other side, Sia-b1 determinants reacting with postinfection CAs share the characteristics of I determinants, with the exception that Sia-b1 determinants require sialyl groups as an immunodominant component. Five sera containing coexisting anti-Sia-b1 and anti-I CAs were tested against Oh and enzyme-treated group O red cells. The results are consistent with a postinfection autoimmune response against a sialo-type 2 structure common for Sia-b1 and I determinants, which could serve as a receptor for Mycoplasma pneumoniae.
Including data from the literature, the repertoire of the light-chain variable domain in pathological anti-Pr cold agglutinins exhibits a clear bias towards the use of the single germline gene-derived subgroup, Vkappa IV (eight of 17 or 47%). The association of Vkappa IV subgroup light chain-containing anti-Pr cold agglutinins with binding to alpha 2,3-, but not alpha 2,6-linked N-acetyneuraminic acid raises speculations about a possible role of subgroup-derived determinants in anti-Pr binding.
Two IgMa cold agglutinins (CAs) reacted with protease- and sialidase-resistant antigens expressed in equal strength on human adult (I), newborn (i), i adult, rabbit (I) and rhesus monkey (i) erythrocytes. The antibodies were inhibited by the linear type 2 sequence lacto-N-neotetraose and the branched type 2 sequence lacto-N-neohexaose. Endo-ß-galactosidase treatment of red cells, which splits type 2 chains from the surface, abolished CA reactivity. The CAs expressed the idiotype recognized by the anti-idiotype 9G4 specific for anti-I and anti-i CAs. The data suggest that the two CAs recognize linear (i) as well as branched (I) type 2 chains. It is proposed to term these CAs anti-j.
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