[Studies on an extract from Haemophilus influenzae type a. II.--Phagocytic capacity of sera obtained from rabbits...

Opsonins may protect against infections. In this study, the different parameters of opsonization assay are strictly standardized. Results are expressed as percentage of opsonization. 0% and 100% opsonization must be established. The experiment without immunserum is used as the 0% opsonization. To determine the 100% opsonization an excess of reducing capacity is required. This is provided by crushed leukocytes. Rabbits are immunised by bacterial extract from Haemophilus influenzae type a. The hemagglutinins are detected in sera earlier (D + 30) and longer than the opsonic activity. Phagocytosis increases from the second month following the immunization. Percentage of opsonization is maintained at about 50% up to the sixth month. Alternatively, the percentage of phagocytosis is decreasing when heterologous bacteria are used. The serum thermolabile factors are necessary for the response. The phagocytic capacity is not modified whether leukocytes are obtained from immunized rabbits or not.