Kalmar "B cell" gabaɗaya tana nufin wani nau'in farin jini, wanda kuma aka sani da B lymphocyte, wanda ke taka muhimmiyar rawa a cikin martanin tsarin rigakafi ga abubuwan waje, kamar ƙwayoyin cuta da ƙwayoyin cuta. Kwayoyin B suna da alhakin samar da ƙwayoyin rigakafi, waɗanda sune sunadaran da zasu iya ganewa da kuma kawar da takamaiman antigens. Wadannan antigens na iya kasancewa daga kwayoyin cuta ko daga wasu abubuwa na waje, irin su gubobi ko allergens. Kwayoyin B suna kuma shiga cikin tsarin ƙwaƙwalwar rigakafi, wanda ke ba da damar tsarin rigakafi don tunawa da amsa da sauri ga antigens da aka ci karo da su a baya.