Alveolar structure of salivary glands of the lone star tick, Amblyomma americanum (L.): unfed females.

Alveoli in the salivary glands of unfed Amblyomma americanum (L.) females (postnymphal ticks that had not yet taken a bloodmeal as an adult) were studied. As in other species of female ixodid ticks, the salivary glands consisted of three alveoli, one agranular and two granular. The agranular alveoli were directly attached to the anterior portion of the main salivary duct, consisted of approximately 13 to 14 cells, and were without valves. Six peripheral cells had tortuous, plasma membrane infoldings with closely associated mitochondria, an abundance of lipidlike droplets and relatively flat apical surfaces. A relatively large, clear, "central" cell occupied most of the alveolar midsection. The "central" cell made contact with the alveolar tubular lumen through an opening of a previously undescribed, concentric, myoepithelial-like cell that we call a "constrictor" cell. Granular alveoli consisted of approximately 14 to 16 cells. Type II granular alveoli have two complex granular cells in close proximity to the cuticular alveolar valve, whereas Type III alveoli have only one. Thin epithelial cells separate adjacent granular cells in both alveolar types and only one "cap" cell with myoepithelial-like features lining the alveolar lumen in weblike fashion was present. We hypothesize that the cap cell may play a significant role in helping propel secretions from alveoli to associated ducts.