Erythrocytes possessing the A antigen can be sub divided into A1 and A2 cells. Anti- A1 Lectin is designed for use in agglutination tests for the detection of the A1 antigen on human red cells. Group A red blood cells which are agglutinated with Anti- A1 Lectin are said to be of sub-group A1.Those which are not agglutinated by Anti-A1 Lectin fall into subgroups weaker than A1, the majority being classified as A2. Approximately 80 % of the population of blood group A is A1, while the remaining 20% are A2 or weaker subgroup.
The procedure used with this reagent is based on the principle of agglutination described by Landsteiner. Normal human red blood cells possessing antigens will clump in the presence of antibody directed towards the antigens. Renkonen showed that some extracts of seeds (lectin) contain powerful agglutinins with human blood group specificity. The extract of the seeds from Dolichos biflorus is virtually specific for A1 antigen on red blood cells.