Hyperphagocytic haemocytes in Manduca sexta

Area of Science:

• Insect immunology
• Cell biology
• Invertebrate pathology

Background:

• Haemocytes are crucial for invertebrate immune responses.
• The specific roles and diversity of haemocyte types in insects are not fully understood.
• The tobacco hornworm moth (Manduca sexta) is a model organism for insect immunity studies.

Purpose of the Study:

• To identify and characterize novel haemocyte types in Manduca sexta larvae.
• To investigate the phagocytic capabilities and functions of these newly discovered haemocytes.
• To elucidate the role of these cells in the insect immune response and nodule formation.

Main Methods:

• Isolation and characterization of haemocytes from Manduca sexta larvae.
• In vitro phagocytosis assays using bacteria (E. coli, S. aureus) and microspheres.
• Microscopy to observe cell morphology and behavior.
• Analysis of haemocyte distribution and function in infected and non-infected insects.

Main Results:

• Discovery of a novel haemocyte type, termed hyperphagocytic cells (HP), in Manduca sexta larvae.
• HP cells demonstrate extreme phagocytic capacity, engulfing up to 500 bacteria per cell.
• HP cells are responsible for sequestering the majority of bacteria, despite comprising only 1% of circulating haemocytes.
• Phagocytosis by HP cells is involved in early stages of nodule formation.
• HP cells exhibit a distinct spreading morphology in non-infected insects, which is impaired after hyperphagocytosis.

Conclusions:

• A dedicated class of "professional" phagocytic haemocytes has been identified in an invertebrate for the first time.
• These hyperphagocytic cells play a significant role in the immune defense of Manduca sexta.
• HP cells are critical for bacterial clearance and contribute to the formation of immune structures like nodules.