Haemoglobin Inhibits the Development of Infective Promastigotes and Chitinase Secretion in Leishmania Major Cultures

Haemoglobin or blood in the growth medium of Leishmania major inhibited the formation of infective promastigotes and the secretion of chitinases. Inoculation of mice with stationary-phase parasites from control medium caused infections in 20/29 mice, compared to 3/20 mice injected with parasites grown with 10% rabbit blood, or 1/30 mice that received parasites grown with rabbit haemoglobin. The concentration of peanut lectin (PNA) required to agglutinate promastigotes was used as an index of their infectivity, ranging from a high concentration for infective populations to a low concentration for relatively non-infective populations. Agglutination of 50% of the parasites from control medium or from medium containing rabbit haemoglobin required 4.1 fig PNA/ml and 0.1 fig PNA/ml, respectively. Chitinase activities/10⁷ parasites decreased from 4.8 units chitinase and 12.5 units N-acetylglucosaminidase (NAGase) in the control to 2.0 units chitinase and 8.5 units NAGase in cultures containing rabbit haemoglobin. Rabbit, human, bovine and pigeon haemoglobins had various inhibitory effects on the activity of chitinases and not on the virulence, as expressed by PNA agglutination. The relevance of the results to the cycle of Leishmania is discussed.