Deficiencies in any of the defense mechanisms of the host can lead to severe microbial infections; these are of clinical relevance. Broad up-to-date knowledge in this field allows identification of many unspecific as well as highly specific defense reactions involved in the struggle against infectious diseases. On the other hand, protective structures on the microbial cell surfaces have been adapted and improve the counterpart's chances of survival. In particular, it has been considered that the great diversity of the bacterial envelopes not only determines the anatomical location of the tissue injury but also induces activation of distinct parts of the complex defense system. The specific defense mechanism, whose most prominent constituent is provided by the antibo