International Science Community Association International Research Journal of Biological Sciences 14 2 2025 05 10 Investigating the haemocyte - mediated immune response in American cockroach (Periplaneta americana) to Escherichia coli infection 30 36 EN D. Doshita 1 Department of PG studies in Biotechnology, Nrupathunga University, NT road, Bangalore, India Khanum Saniya 2 Department of PG studies in Biotechnology, Nrupathunga University, NT road, Bangalore, India H. Anusha 3 Department of PG studies in Biotechnology, Nrupathunga University, NT road, Bangalore, India Khabade Sarina P. 4 Department of PG studies in Biotechnology, Nrupathunga University, NT road, Bangalore, India A. Geeta Rautela 1 Department of Botany, Aligarh Muslim University, Aligarh, Uttar Pradesh, India B. Rose Rizvi 2 Department of Botany, Aligarh Muslim University, Aligarh, Uttar Pradesh, India Samantaray Debajani 1 Plant Pathology and Microbiology Division, Regional Plant Resource Centre, Bhubaneswar, Odisha, India Mishra Atmaja Elina 2 Plant Pathology and Microbiology Division, Regional Plant Resource Centre, Bhubaneswar, Odisha, India Panda Subhransu 3 Siksha ‘O’ Anusandhan University, Bhubaneswar, Odisha, India Mohapatra Himadri Das 4 Siksha ‘O’ Anusandhan University, Bhubaneswar, Odisha, India Gupta Nibha 5 Plant Pathology and Microbiology Division, Regional Plant Resource Centre, Bhubaneswar, Odisha, India Sardar Shatavisa 1 Post Graduate Department of Zoology, Barasat Govt. College; 10, K.N.C. Road, Barasat, 24 Pgs North, Kolkata-700124, West Bengal, India Paul Sneha 2 Post Graduate Department of Zoology, Barasat Govt. College; 10, K.N.C. Road, Barasat, 24 Pgs North, Kolkata-700124, West Bengal, India Ghosh Jayati 3 Post Graduate Department of Zoology, Barasat Govt. College; 10, K.N.C. Road, Barasat, 24 Pgs North, Kolkata-700124, West Bengal, India > Research Paper 2025 2 5 2025 05 10 The immune system of the American cockroach (Periplaneta americana) is primarily innate, relying on various cellular and humoral responses to defend against pathogens. Haemocytes play a central role in the cockroach's immune system, acting as the primary cells involved in defence mechanisms such as phagocytosis, encapsulation, and the production of immune molecules. In the present study, the impact of bacterial infection on haemocyte-mediated immune responses in Periplaneta americana was studied. For the experiment, laboratory-cultured Gram-negative bacteria, Escherichia coli, were injected into the abdominal cavity of the insect. Haemolymph was collected 2 hours, 5 hours, and 24 hours post-infection from the treated and control adult cockroaches, and morphological changes were noted. Total haemocyte counts (THC) and differential haemocyte counts (DHC) were also compared between control and inoculated host specimens. THC levels rose at 2 hours of infection, reached a significant peak at 5 hours of infection, and declined at 24 hours of infection. A significant decline in the number of prohaemocytes and an increase in granulocytes were found throughout the infection period. Among all the haemocytes, granulocytes were identified as the major defense cell, presenting an elevated cell count and being associated with aggregation at the site of infection, vacuolation related to phagocytosis, and also being involved in the formation of thin, finger-like extracellular traps. Copyright@ International Science Community Association