Lymphoid cells include T cells, B cells, natural killer cells, and innate lymphoid cells. Lymphoid tissue is also associated with mucosas such as mucosa-associated lymphoid tissue (MALT). Immune cells can be divided into myeloid cells and lymphoid cells. Myeloid and lymphoid lineages both are involved in dendritic cell formation. Follicular hyperplasia is a type of lymphoid hyperplasia. Germinal centers may form with the progression of lymphoid infiltrate resulting in acinar atrophy. Recent studies have suggested they arise distinctly from the lymphoid and myeloid lineages. Canine distemper virus tends to orient its infection towards the lymphoid, epithelial, and nervous tissues. It may be lymphoid or myeloid. Other kinds of connective tissues include fibrous, elastic, and lymphoid connective tissues. Sarcoid has tight epithelioid granulomas and lymphoid infiltrate. These fish rely on regions of lymphoid tissue within other organs to produce immune cells. The spleen is the largest collection of lymphoid tissue in the body. The disease was characterized by fever, oral erosions, diarrhea, lymphoid necrosis, and high mortality. The submucosa contains aggregates of lymphoid tissue.