Factors affecting the capacity of Theileria annulata sporozoites to invade bovine peripheral blood lymphocytes.

The number of T. annulata sporozoites invading bovine peripheral blood lymphocytes (PBL) under different conditions (in vitro) was determined. Heat-inactivation of T. annulata sporozoites for 45 min, in a thermostatically controlled, shaking water bath preset and stabilised at 60 degrees C resulted in an almost total lack of invasion of fresh, normal PBL by the sporozoites, indicating that the interiorization process is parasite-effected. The mean number of T. annulata sporozoites interiorization (per 1000 lymphocytes) in cultures set up using sporozoites and PBL, mixed and incubated at 0 degrees C for 1 h in melting ice, was highly significantly reduced (P less than 0.01), indicating the invasion of bovine lymphocytes by T. annulata sporozoites is an active process dependent on active metabolism which is markedly affected by temperature. Pre-treatment of PBL with trypsin significantly reduced the number of invading sporozoites thus incriminating proteins or glycoproteins as constituents of receptors involved in sporozoite-lymphocyte recognition.