The common cell types in connective tissue include: fibroblasts, mast cells, plasma cells, macrophages, adipocytes, and leukocytes.
Fibroblasts are the most common cell type of connective tissue. They produce both fibers and amorphous ground substance. Typically only the oval nuclei are visible. These cells are found associated with the fibers listed above. In the tendon, fibroblasts are seen as elongate nuclei found sandwiched between collagen fibers.
Mast Cells are round/oval cells that contain granules that are metachromatic because of their glycosaminoglycan content; these cells are easily seen in the connective tissue spread. The toluidine blue component of the stain applied to this slide renders the mast cell granules blue-purple.
Plasma cells are ovoid with basophilic cytoplasm, due to rER. The diagnostic feature of plasma cells is their eccentric round nuclei commonly described as "clock face" nuclei . This appearance is due to heterochromatin clumps. These cells are readily identified in the mucosa of the digestive tract.
In the lung, alveolar macrophages (dust cells) are found easily in the air spaces where these cells have either ingested carbon particles or erythrocytes. Some may appear as vacuolated cells. One can infer the identity of a macrophage by its indented nucleus . Macrophages are phagocytic cells that are difficult to find in normal tissues because there is not sufficient cause for them to increase in number.
Adipocytes , fat cells are large cells specialized in storage of neutral fats. Lipid is removed in routine tissue preparation. Consequently the cell appears as a thin rim of cytoplasm surrounding the vacuole of dissolved lipid. The nucleus is eccentric and flattened. Adipose tissue is a connective tissue with a predominance of adipocytes.
Leukocytes are white blood cells that are readily found in connective tissue. Lymphocytes (similar in size to red blood cells) are the most common connective tissue leukocyte. Aggregates of lymphocytes are often found associated with the mucosal epithelium of the GI tract, such as this slide of the esophagus. They have a small amount of slightly basophilic cytoplasm and a large, darkly stained nucleus because of condensed chromatin.