Enhancement of nonspecific immunity to Klebsiella pneumoniae infection by a synthetic immunoadjuvant (N-acetylmuramyl-L-alanyl-D-isoglutamine) and several analogs.

N-Acetylmuramyl-L-alanyl-D-isoglutamine and four other synthetic adjuvants that are structural analogs of part of the mycobacterial peptidoglycan monomer are shown to enhance the nonspecific immunity of mice infected by Klebsiella pneumoniae. These compounds are active by various routes, including oral administration; they are also effective when administered after challenge. Of the seventeen other analogs tested, none is able to increase significantly resistance to infection, although seven of these molecules are adjuvant-active in saline. Previous results have shown that in contrast to lipopolysaccharides, these synthetic adjuvants are devoid of immunogenicity, mitogenicity, and toxicity in normal or adrenalectomized mice.