The effective adsorption of rPA83m, rPA1+2 and rPA3+4 to SPs while maintaining the antigenic specificity of modified anthrax antigens within SPs-antigen compositions, and the possibility of SPs to stabilise non-modified rPA83, have encouraged consideration of the influence of SPs on the stability of each of three modified antigens. Here, RPA1 is linked to anthrax infection.