An isolated and purified non-denatured transferrin receptor protein of a Moraxella strain, particularly M. catarrhalis, has an apparent molecular mass of about 80 to about 90 kDa, as determined by SDS-PAGE. The transferrin receptor protein or a fragment analog thereof is useful in diagnostic applications and immunogenic compositions, particularly for in vivo administration to a host to confer protection against disease caused by a strain of Moraxella.