Biofilm protect bacteria against immune system and antibiotic therapy. What's your question exactly? 

Biofilm consists matrix that mostly are polymeric glucose or etc that these matrix not antigen.

Biofilm is extracellular protective matrix of microbes are different from their planktonic counterparts in very important ways. First, when microbes live as a community, they become much less susceptible to antibiotics, even if highly susceptible as individual cells. Thus, when microorganisms form a community, they are protected against a variety of antibiotics that clinicians commonly prescribe for their patients. Second, and more the focus of this perspective, these  microorganisms resist attack and killing by the host immune system . Bacteria living as biofilmscause of persistent and destructive inflammatory processes , example of biofilm infections in humans is P. aeruginosa associated with the lungs of cystic fibrosis.

In vitro data indicate that S. aureus biofilms are not inherently protected against the attack by neutrophils or macrophages. Phagocytosis and generation of oxygen radicals was seen, as was clearance of biofilm and release from the neutrophils of DNA,while S. epidermidis biofilms appeared to be less sensitive towards the neutrophil attack, but still clearance of biofilm and phagocytosis was seen. also deposition of C3b, the key complement component, was impaired on S. pneumoniae bio-films.

the results of Domenech etal.,2013  showed that biofilm formation diverts the alternative complement pathway activation by a PspC-mediated mechanism. Furthermore, phagocytosis of pneumococcal biofilms was also impaired. The present study confirms that biofilm formation in S. pneumoniae is an efficient means of evading both the classical and the PspC-dependent alternative complement pathways the host immune system.

review these references 

F. Günther, G. H. Wabnitz, J. W. Costerton, P. Stroh et al., “Host defence against Staphylococcus aureus biofilm infection: Phagocytosis of biofilms by polymorphonuclear neutrophils (PMN),” Molecular Immunology, vol. 46, no. 8-9, pp. 1805–1818, 2009.

F. Guenther, P. Stroh, C. Wagner, U. Obst, and G. M. Hänch, “Phagocytosis of staphylococci biofilms by polymorphonuclear neutrophils: S. aureus and S. epidermidis differ with regard to their susceptibility towards the host defense,” International Journal of Artificial Organs, vol. 32, no. 9, pp. 565–573, 2009.

E. Meyle, P. Stroh, F. Günther, T. Hoppy-Tichy, C. Wagner, and G. M. Hänsch, “Destruction of bacterial biofilms by polymorphonuclear neutrophils: relative contribution of phagocytosis, DNA release, and degranulation,” International Journal of Artificial Organs, vol. 33, no. 9, pp. 608–620, 2010.

 Thanks Dr. Abed for sharing useful information.