There are three major types of cells in the lymphoid tissues of the body. One category, the ____________, contains immunocompetent cells that are able to destroy or immobilize foreign substances in the body; these foreign substances are called ____________. The two varieties in this group are ______________ and _____________. The other class of protective cells are called _______________. These defend the body by engulfing, or ______________, foreign substances. The third cellular group are the _____________, fibroblast-like cells that form the stroma or framework of the lymphoid organs. Lymphoid tissue is specifically classified as a type of connective tissue called ____________. When lymphoid tissue is loosely packed, it is called ______________; when it is tightly packed into spherical masses, the arrangement is said to be ________________.