The invention relates to methods and products for regulating lectin complement pathway associated complement activation. The methods include both in vitro and in vivo methods for inhibiting lectin complement pathway associated complement activation. The methods are accomplished by contacting a mammalian cell having surface exposed MBL ligand with an effective amount of a mannan binding lectin inhibitor to inhibit lectin complement pathway associated complement activation. The mannan binding lectin inhibitor may be administered to a subject to prevent cellular injury mediated by lectin complement pathway associated complement activation. The products of the invention include compositions of a mannan binding lectin inhibitor. The mannan binding lectin inhibitor is an isolated mannan binding lectin binding peptide that selectively binds to a human mannan binding lectin epitope and that inhibits lectin complement pathway associated complement activation. The products also include hybridoma cell lines and pharmaceutical compositions.