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Anti-deoxyadenylate antibodies were produced in rabbits by injecting a conjugate of deoxyadenosine 5′-phosphate with bovine serum albumin. The antisera, as analyzed by double diffusion in agar and the quantitative precipitin reaction, showed hapten-specific antibodies. The specific interaction between [3H]deoxyadenylate and antiserum was studied by a sensitive nitrocellulose membrane-binding assay. The specificity of the antibodies was analyzed by measuring the effectiveness of other nucleotides or derivatives to inhibit the hapten-antibody binding. The requirements for recognition by the antibody sites were studied by using a series of naturally occurring nucleic acid components as well as some synthetic derivatives as inhibitors. The antibodies were found to show a high degree of specificity for the whole nucleotide, the base, sugar and phosphate playing almost equally important roles. There was cross reactivity with other mononucleotides, although of a low order. The antibodies were able to react with DNA and tRNA.

The cross reactivity between P. vivax and P. falciparum was studied by an indirect fluorescent antibody (FA) technique in which homologous and heterologous antigen-antibody systems were used. Two modifications of the previously described test were employed: (1) the use of liquid nitrogen for the preservation of parasitized whole blood for use as the source of antigen, and (2) the use of Evans blue as a counterstain to decrease the intensity of nonspecific fluorescence. Six of 29 sera from natural P. vivax infections reactive with P. vivax antigen were also reactive with P. falciparum antigen. Eleven of 21 serologically positive sera from natural P. falciparum infections were reactive with P. vivax antigen, two of these with the P. vivax antigen only. Two groups of sera from human volunteers with either P. vivax or P. falciparum infections were titrated in parallel tests with homologous and heterologous antigen. In the first series the geometrical mean reciprocal titers (GMRT's) with P. falciparum, sera were 28.3 for the homologous antigen and 6.3 for the heterologous antigen. For the P. vivax sera the values were 17.2 and 9.3 for the homologous and heterologous cases, respectively. In the second series the values for the P. falciparum sera were 132 with the homologous antigen and 20.0 with the heterologous antigen; the P. vivax sera gave values of 30.0 and 11.9 with the homologous and heterologous antigens, respectively. A comparison of titers of blood collected on filter paper and matched serum samples from subjects with P. vivax or P. falciparum infections revealed GMRT's of 24.2 for the blood and 41.0 for the serum. Specificity tests of 246 sera from subjects presumptively free of malaria revealed 28 positive reactions. It is concluded that there is both a species-specific and a group-specific component in the reaction of these two organisms. The specificity of the reaction and the usefulness of the filter paper method of blood collection have been confirmed.