Observations on Sensitization of Guinea Pigs with Alum-Precipitated Ragweed Extract

Alum-precipitated ragweed pollen extract is a potent antigen for producing anaphylactic sensitization in guinea pigs, 1-4 whereas the watery extract is by comparison a poor one. Alum-precipitated extracts have been successfully applied in sensitizing guinea pigs to house dust 5-8 and cotton linters 5 , 6 , 9 and in sensitizing dogs to horse serum. 10 The enhanced antigenic response of the alum-precipitated extract is generally attributed to two factors: first, retention of the antigenic substance by the precipitate so that it is only slowly liberated into the system, thus producing a continuous stimulation for the production of antibodies; and second, the local tissue response to the precipitate at the site of injection is said to delay absorption of the antigen. Thus diphtheria toxoid has been detected at the site of injection from a few days to several weeks after administration of alum-precipitated toxoid. 11 , 12 The experiments recorded here were designed to determine whether antigenic constituents of ragweed pollen could be detected in the indurated nodule that forms at the site of injection of the alum precipitate in guinea pigs and persists for several months.

Experimental. An alum-precipitated ragweed pollen extract (1-20 dilution) was prepared in the manner previously described. 6 For sensitizing, 1 ml of the whole alum-treated extract was employed for subcutaneous injection because it was found that the antigenic constituents were not completely precipitated by the alum. Thus precipitates, separated by centrifugation from two 1 ml aliquots of the alum suspension, were suspended in 0.9% sodium chloride and injected subcutaneously into 2 normal guinea pigs. The supernatant solutions, without further treatment, were likewise injected into 2 normal animals.