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Encapsulation in insects; a review
Vol. 9, No. 1
ENCAPSULATION
173
SESSION 6 : THE ENCAPSULATION PROCESS ENCAPSULATION IN INSECTS; A REVIEW. P. G6tz, Free U n i v e r s i t y of Berlin (West), Germany Encapsulation consists of the formation of an envelope around foreign objects such as parasites, implanted tissues or particulate materials. Most often this envelope is formed by attaching blood cells. A tentative scheme of events occuring during cellular encapsulation is presented: 1. Cellular encapsulation is triggered after random contact of blood cells with foreign surfaces. 2. Granular cells (GR) react by degranulation. 3. The discharged material sticks to the foreign surfaces and to the GRs. 4. GRs disintegrate. 5. D i s c h a r g i n g / d i s i n t e g r a t i n g GRs attract and activate plasmatocytes (PL). 6. Activated PLs spread over surfaces with attached material from GRs. 7. Attached PLs continuously flatten and establish cell to cell contact. 8. Melanization starts from the material discharged from GRs. 9.Electron dense material (melanin?) appears in the extracellular spaces between flattened PLs. 10. Outermost PLs leave the capsule. Critical discussion is neccessary to establish whether the above sequence of events is generally applicable to insects and perhaps to other arthropods. Possible contradictions should cause the planning of crucial experiments to clarify the situation. Comparative investigation of humoral encapsulation in insects and the phenoloxidase system in arthropods promises essential information for the understanding of the basic mechanisms which rule the cellular defense reactions in insect hemocoel.
INITIATION AND CESSATION OF HAEMOCYTIC ENCAPSULATION IN THE LOCUST SCHISTOCERCA GREGARIA AND IN THE COCKROACH PERIPLANETA AMERICANA. Ann Lackie and Garry Takle, University of Glasgow, Scotland. The extent of haemocytic adhesion in vitro and thickness of encapsulation in vivo varies with the wettability of the foreign surface, both inter- and intra-specifically (Lackie, 1983; J.Cell Sci. 63, 181). Negatively-charged beads are not encapsulated in the locust, and the point at which the response is 'switched on' lies close to neutrality. Investigation of haemocyte surface-charge by cell microelectrophoresis and by binding of cationised ferritin reveals that locust haemocytes are significantly more negatively-charged than cockroach cells; this may explain why locust cells do not adhere to negatively-charged foreign surfaces, and why ~mmunorecognition of biotic implants is poor in this species. Haemocytic capsules are generally thicker in cockroaches than in locusts; measurements on blood volume using H-inulin, haemocyte counts and hence calculations of total haemocyte numbers, show that cockroaches have a greater proportion and number of plasmocytes. Recruitment (see abstract by Takle) ceases within about 24 h, and the capsule surface becomes covered with sheets of coating material which, in common with the host's subepidermal connective tissue, bind alcian blue. This material is presumably treated as 'self' by the immunorecognition system; coated capsules from Periplaneta, transplanted into Schistocerca, do not - in common with tissue transplants from the same donor - stimulate a haemocytic response.
ENCAPSULATION
173
SESSION 6 : THE ENCAPSULATION PROCESS ENCAPSULATION IN INSECTS; A REVIEW. P. G6tz, Free U n i v e r s i t y of Berlin (West), Germany Encapsulation consists of the formation of an envelope around foreign objects such as parasites, implanted tissues or particulate materials. Most often this envelope is formed by attaching blood cells. A tentative scheme of events occuring during cellular encapsulation is presented: 1. Cellular encapsulation is triggered after random contact of blood cells with foreign surfaces. 2. Granular cells (GR) react by degranulation. 3. The discharged material sticks to the foreign surfaces and to the GRs. 4. GRs disintegrate. 5. D i s c h a r g i n g / d i s i n t e g r a t i n g GRs attract and activate plasmatocytes (PL). 6. Activated PLs spread over surfaces with attached material from GRs. 7. Attached PLs continuously flatten and establish cell to cell contact. 8. Melanization starts from the material discharged from GRs. 9.Electron dense material (melanin?) appears in the extracellular spaces between flattened PLs. 10. Outermost PLs leave the capsule. Critical discussion is neccessary to establish whether the above sequence of events is generally applicable to insects and perhaps to other arthropods. Possible contradictions should cause the planning of crucial experiments to clarify the situation. Comparative investigation of humoral encapsulation in insects and the phenoloxidase system in arthropods promises essential information for the understanding of the basic mechanisms which rule the cellular defense reactions in insect hemocoel.
INITIATION AND CESSATION OF HAEMOCYTIC ENCAPSULATION IN THE LOCUST SCHISTOCERCA GREGARIA AND IN THE COCKROACH PERIPLANETA AMERICANA. Ann Lackie and Garry Takle, University of Glasgow, Scotland. The extent of haemocytic adhesion in vitro and thickness of encapsulation in vivo varies with the wettability of the foreign surface, both inter- and intra-specifically (Lackie, 1983; J.Cell Sci. 63, 181). Negatively-charged beads are not encapsulated in the locust, and the point at which the response is 'switched on' lies close to neutrality. Investigation of haemocyte surface-charge by cell microelectrophoresis and by binding of cationised ferritin reveals that locust haemocytes are significantly more negatively-charged than cockroach cells; this may explain why locust cells do not adhere to negatively-charged foreign surfaces, and why ~mmunorecognition of biotic implants is poor in this species. Haemocytic capsules are generally thicker in cockroaches than in locusts; measurements on blood volume using H-inulin, haemocyte counts and hence calculations of total haemocyte numbers, show that cockroaches have a greater proportion and number of plasmocytes. Recruitment (see abstract by Takle) ceases within about 24 h, and the capsule surface becomes covered with sheets of coating material which, in common with the host's subepidermal connective tissue, bind alcian blue. This material is presumably treated as 'self' by the immunorecognition system; coated capsules from Periplaneta, transplanted into Schistocerca, do not - in common with tissue transplants from the same donor - stimulate a haemocytic response.