is ▁cells . ▁ ▁The ▁binding ▁of ▁b acter ial ▁surface ▁re cept ors ▁for ▁ad hes ion ▁has ▁also ▁been ▁imp licated ▁in ▁the ▁formation ▁of ▁bio fil ms . ▁ ▁Rec ogn ition ▁of ▁red ▁blood ▁cells ▁▁ ▁Blood ▁types ▁ ▁Red ▁blood ▁cells ▁contain ▁ant ig ens ▁in ▁their ▁pl asma ▁memb ran es ▁that ▁distinguish ▁them ▁as ▁part ▁of ▁a ▁specific ▁category ▁of ▁blood ▁cell . ▁These ▁ant ig ens ▁can ▁be ▁pol ys ac char ides , ▁g ly cop rote ins , ▁or ▁G PI ▁( a ▁g ly col ip id ) ▁- link ed ▁prote ins . ▁ ▁Ant ig ens ▁range ▁in ▁complexity , ▁from ▁small ▁mole cules ▁bound ▁to ▁the ▁ext rac ell ular ▁side ▁of ▁the ▁ph osph ol ip id ▁bil ayer , ▁to ▁large ▁memb rane ▁prote ins ▁that ▁loop ▁many ▁times ▁between ▁both ▁sides ▁of ▁the ▁memb rane . ▁ ▁The ▁smaller ▁pol ys ac char ide ▁ant ig ens ▁class ify ▁blood ▁cells ▁into ▁types ▁A , ▁B , ▁AB , ▁and ▁O , ▁while ▁the ▁larger ▁protein ▁ant ig ens ▁class ify ▁blood ▁cells ▁into ▁types ▁Rh ▁D - pos itive ▁and ▁Rh ▁D - negative . ▁While ▁the ▁bi ological ▁role ▁of ▁the ▁correct ▁blood ▁type ▁is ▁unclear ▁and ▁may ▁be ▁v estig ial , ▁the ▁consequences ▁of ▁incorrect ▁blood ▁types ▁are ▁known ▁to ▁be ▁severe . ▁ ▁The ▁same ▁cells ▁that ▁recognize ▁PA MP s ▁on ▁micro b ial ▁path og ens ▁may ▁bind ▁to