Increased elongated and stabilized microtubules in psoriatic keratinocytes.

Microtubules (MT) occur in the keratinocytes as 20 nm broad tubular structures with an electron-lucent core surrounded by an electron-dense wall. The number and the length of the MT increased to the upper epidermal layers. In the normal keratinocytes the MT were relatively short (maximal length 2.2 microns) and slightly tortuous. Their outline was tenuous and irregular. Sometimes the MT were interrupted indicating a high fragility. In the upper layers of the psoriatic epidermis the MT reached a maximal length of 3.1 microns, showing a greater elongation than in the normal epidermis. The MT were stright and distinctly limited, most likely resulting from a higher grade of stabilization or polymerisation. By their interaction with the tonofilaments the MT may contribute to the stability of the cell shape, delaying the flattening of the psoriatic keratinocytes in the upper epidermal layers. Nowhere did the MT make direct contact with the cell membrane. At some places they did gain access to the cell membrane by short microfilaments.