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General remarks and conclusions ISDCI invertebrate immunology conference
Vol. 9, No.
1
GENERAL
REMARKS
183
GENERAL REMARKS AND CONCLUSIONS
ISDCI INVERTEBRATE IMMUNOLOGY CONFERENCE
From all over the world, but mainly from European institutes, 77 participants had come to this interesting and rewarding conference on invertebrate immunology. On the basis of 7 review papers, 31 communications and 15 posters, the following 7 topics have been intensively discussed: i. morphology and biochemistry of hemocytes; 2. hemogramme and its endocrine control; 3. the phenoloxydase system in immune reactions; 4. the antibacterial molecules; 5. the immunorecognition process; the encapsulation process; 7. cellular and humoral reactions of immunity. We will not discuss the actual information that was presented in the sessions as it is impossible to do so in brief (the abstracts will be published in DCI). We will therefore try to depict which topics and ideas appeared to be of predominant and general interest. Classification and nomenclature of insect haemocytes has always been difficult. It still is, since even among the small number of insect immunologists present at a round table discussion on this subject, in spite of the fact that all had the intention to come to an agreement, it was impossible to decide what terminology has to be used. Still, it was agreed that the use of names of vertebrate blood cells should be avoided in order to prevent spreading the idea that certain insect hemocytes would be homologues of vertebrate granulocytes, macrophages or lymphocytes. By using separate names for invertebrate blood cells we are able to indicate the typical features of these cells. One important thing we have learned is that we must not use only one parameter to characterize invertebrate blood cells; we have to combine several techniques - e.g. morphological, enzyme cytochemical, immunocytochemical, cinematographic methods - in order to come to a description of the various types of hemocytes. Moreover, a quantitative approach in addition to qualitative methods is of great importance. It was felt that more insight is needed into the functions that are exerted by the morphologically distinguished cell types, and that this insight can be gained only by in vitro studies of pure cell populations. These can be obtained by isolation and separation of hemocytes from blood or tissues. Two methods to do this have been discussed: i. cell separation by centrifugation on continuous and discontinuous gradients and 2. cell separation using monoclonal antibodies against surface determinants of the different hemocyte types.
184
CONCLUSIONS
Vol.
9, No.
1
An interesting field appears to be the interactions between the immune and the endocrine system. Several speakers have shown that hormones and parasites may influence the immune system. Publications on parasite - host interactions strongly suggest that parasites ~ have some effects on the neuroendocrine system and possibly via that on the immune system. Especially the role of (neuro) hormones, already isolated in pure form in insects and snails, in the proliferation and differentiation of defence cells seems to be a good field for further research. Immunoendocrinology is still a black box, but an intriguing one. Once again it became clear that still little is known of blood cell formation in invertebrates. Hemocytes are usually present - besides in the circulation - in connective tissue; in some cases special areas or even organs are found that are designated as hemopoietic and (putative) stem cells are thought to be present there. With respect to circulating hemocytes, it is clear that among the various morphological types one is usually present which is regarded as a circulating progenitor cell (e.g. the prohemocyte in arthropods and the 'round hemocyte' in molluscs). However, the incontrovertible demonstration of the origin of the other cell types to which a number of functions can be assigned, is still lacking. Concerning plasma or serum factors the following can be said. We have seen that there is a variety of humoral defence factors in invertebrates. Although these factors have a broad specificity, they are efficiently directed against practically all types of invaders. These factors can be divided in 2 groups: i. factors with direct effects on foreign bodies (lytic enzymes, inhibitors of bacterial growth etc.) and 2. factors that work indirectly (mediators) e.g. the phenoloxydase system and lectins (agglutinins, opsonins). The biochemistry and modes of action of the molecules from the first group have been discussed for insects and annelids. Of molecules of the second group, also the biochemistry was subject of discussion; however, most attention was paid to the role of these molecules in direct humoral defence activities and their involvement in coagulation, cell-cell communication, cell migration, recognition of foreigness, hemocytic nodule formation, phagocytosis and encapsulation. With respect to the site of synthesis of all these factors a role for both circulating and tissue cells has been indicated. Possible tissue sources for defence factors are the hemopoietic tissues, fat body - pericardial - and chloragogue cells. However, to get evidence on the sites of synthesis, again the separation of pure cell populations of hemocytes and tissue cells is needed. This summary was presented after the last paper of the conference. Then, a final round table discussion took place in which many of the above topics passed in review. A scheme, presented earlier on in the conference by Peter G6tz, summarizing the occurrence and characteristics of defence cells and substances throughout the invertebrate kingdom, was discussed and adapted to the new information and views, gathered during this conference. T. Sminia and W.P.W. Faculty of Medicine Free University Amsterdam The Netherlands
van der Knaap
1
GENERAL
REMARKS
183
GENERAL REMARKS AND CONCLUSIONS
ISDCI INVERTEBRATE IMMUNOLOGY CONFERENCE
From all over the world, but mainly from European institutes, 77 participants had come to this interesting and rewarding conference on invertebrate immunology. On the basis of 7 review papers, 31 communications and 15 posters, the following 7 topics have been intensively discussed: i. morphology and biochemistry of hemocytes; 2. hemogramme and its endocrine control; 3. the phenoloxydase system in immune reactions; 4. the antibacterial molecules; 5. the immunorecognition process; the encapsulation process; 7. cellular and humoral reactions of immunity. We will not discuss the actual information that was presented in the sessions as it is impossible to do so in brief (the abstracts will be published in DCI). We will therefore try to depict which topics and ideas appeared to be of predominant and general interest. Classification and nomenclature of insect haemocytes has always been difficult. It still is, since even among the small number of insect immunologists present at a round table discussion on this subject, in spite of the fact that all had the intention to come to an agreement, it was impossible to decide what terminology has to be used. Still, it was agreed that the use of names of vertebrate blood cells should be avoided in order to prevent spreading the idea that certain insect hemocytes would be homologues of vertebrate granulocytes, macrophages or lymphocytes. By using separate names for invertebrate blood cells we are able to indicate the typical features of these cells. One important thing we have learned is that we must not use only one parameter to characterize invertebrate blood cells; we have to combine several techniques - e.g. morphological, enzyme cytochemical, immunocytochemical, cinematographic methods - in order to come to a description of the various types of hemocytes. Moreover, a quantitative approach in addition to qualitative methods is of great importance. It was felt that more insight is needed into the functions that are exerted by the morphologically distinguished cell types, and that this insight can be gained only by in vitro studies of pure cell populations. These can be obtained by isolation and separation of hemocytes from blood or tissues. Two methods to do this have been discussed: i. cell separation by centrifugation on continuous and discontinuous gradients and 2. cell separation using monoclonal antibodies against surface determinants of the different hemocyte types.
184
CONCLUSIONS
Vol.
9, No.
1
An interesting field appears to be the interactions between the immune and the endocrine system. Several speakers have shown that hormones and parasites may influence the immune system. Publications on parasite - host interactions strongly suggest that parasites ~ have some effects on the neuroendocrine system and possibly via that on the immune system. Especially the role of (neuro) hormones, already isolated in pure form in insects and snails, in the proliferation and differentiation of defence cells seems to be a good field for further research. Immunoendocrinology is still a black box, but an intriguing one. Once again it became clear that still little is known of blood cell formation in invertebrates. Hemocytes are usually present - besides in the circulation - in connective tissue; in some cases special areas or even organs are found that are designated as hemopoietic and (putative) stem cells are thought to be present there. With respect to circulating hemocytes, it is clear that among the various morphological types one is usually present which is regarded as a circulating progenitor cell (e.g. the prohemocyte in arthropods and the 'round hemocyte' in molluscs). However, the incontrovertible demonstration of the origin of the other cell types to which a number of functions can be assigned, is still lacking. Concerning plasma or serum factors the following can be said. We have seen that there is a variety of humoral defence factors in invertebrates. Although these factors have a broad specificity, they are efficiently directed against practically all types of invaders. These factors can be divided in 2 groups: i. factors with direct effects on foreign bodies (lytic enzymes, inhibitors of bacterial growth etc.) and 2. factors that work indirectly (mediators) e.g. the phenoloxydase system and lectins (agglutinins, opsonins). The biochemistry and modes of action of the molecules from the first group have been discussed for insects and annelids. Of molecules of the second group, also the biochemistry was subject of discussion; however, most attention was paid to the role of these molecules in direct humoral defence activities and their involvement in coagulation, cell-cell communication, cell migration, recognition of foreigness, hemocytic nodule formation, phagocytosis and encapsulation. With respect to the site of synthesis of all these factors a role for both circulating and tissue cells has been indicated. Possible tissue sources for defence factors are the hemopoietic tissues, fat body - pericardial - and chloragogue cells. However, to get evidence on the sites of synthesis, again the separation of pure cell populations of hemocytes and tissue cells is needed. This summary was presented after the last paper of the conference. Then, a final round table discussion took place in which many of the above topics passed in review. A scheme, presented earlier on in the conference by Peter G6tz, summarizing the occurrence and characteristics of defence cells and substances throughout the invertebrate kingdom, was discussed and adapted to the new information and views, gathered during this conference. T. Sminia and W.P.W. Faculty of Medicine Free University Amsterdam The Netherlands
van der Knaap