Mats W. Johansson

Crustacean haemocytes and haematopoiesis

Crustacean haemocytes play important roles in the host immune response including recognition, phagocytosis, melanization, cytotoxicity and cell-cell communication. Classification of the haemocyte t ...

The prophenoloxidase activating system and its role in invertebrate defence.

Invertebrates have an open circulatory system and must therefore have rapid and immediate noninducible defence and coagulation mechanisms to entrap parasites and prevent blood loss after wounding. As in most animals, these processes are mainly carried out by the blood cells or, as they are called in arthropods, hemocytes. The hemocytes of arthropods and other invertebrates have been shown to be important in defence, since they are responsible for phagocytosis of small foreign particles such as bacteria or fungal spores and form capsules around parasites that are too large to be internalized by individual hemocytes. Because the hemocytes obviously can react to and remove a foreign particle that has succeeded in gaining entry into the body cavity of an arthropod, it appears as if these animals can differentiate non-self from self, and thus a system that can carry out this process ought to be present. Agglutinins or lectins may be one candidate for such a system.l-s Another likely candidate is the so-called prophenoloxidase (proPO) activating system: and recently evidence has accumulated mainly from work done on crustaceans that this may be the case. The prime reason why this system early was proposed to function in recognizing foreign particles was the finding that the enzyme phenoloxidase in crayfish blood was turned into its active form by fungal cell wall p-1,3-gl~cans.~~* This was later also confirmed to be the case in several insect species”” and other in~ertebrates.l~-’~ Other microbial products such as lipopolysaccharides and peptidoglycans from bacterial cell walls are also active as elicitors of the proPo system.*s.16 Thus, regardless of which events follow after the proPo system is activated, it is clear that it can react to foreign microbial polysaccharides and as such can be defined as a recognition system. Recent research has also provided clear evidence that, upon activation of the proPo system, factors are produced that will aid in the elimination of foreign particles such as parasites within the body cavity. This brief overview will report some of these studies, which have mainly been carried out on arthropods, and where

Cell adhesion molecules in invertebrate immunity

Cell adhesion is essential in immunity in invertebrates, e.g., in the cellular immune responses of encapsulation and nodule formation. Here cell adhesion molecules shown or suggested to be involved in invertebrate immunity are reviewed. Blood cells of the crayfish, Pacifastacus leniusculus, can release a cell-adhesive and opsonic peroxidase, peroxinectin. A site containing the motif, KGD, appears to be adhesive by binding to a transmembrane receptor of the integrin family on the blood cells. Peroxinectin also binds a peripheral blood cell surface CuZn-superoxide dismutase. The peroxidase-integrin interaction appears to have evolved early and seems conserved; human myeloperoxidase supports cell adhesion via the alphaMbeta2 integrin. There is evidence for peroxinectin-like proteins in other arthropods. Effects by RGD peptides indicate that integrins mediate blood cell adhesion and cellular immunity in diverse invertebrate species. Other invertebrate blood cell molecules proposed to be involved in adhesion include the insect plasmatocyte-spreading peptide, as well as soluble and transmembrane proteins which show some similarity to vertebrate adhesive or extracellular matrix molecules. Proteins such as the Ig family member hemolin, or proteins found in insects that are hosts for parasitic wasps, inhibit cell adhesion and may regulate or block cellular immunity.

Exocytosis and uptake of bacteria by isolated haemocyte populations of two crustaceans: evidence for cellular co-operation in the defence reactions of arthropods

SummaryThe role of exocytosis in the cellular defence reactions of arthropods was investigated using in vitro cultures of isolated haemocytes (blood cells) from the freshwater crayfish Pacifastacus leniusculus, and the shore crab Carcinus maenas. In both species, activated lysates of those cell types that contain the prophenoloxidase activating system (granular cells of crab and crayfish and semigranular cells of crayfish) were found to induce degranulation (exocytosis) of semigranular and granular cells. A cell lysate, in which the prophenoloxidase system was kept inactive, did not have this effect. Limited degranulation of granular cells of crab was also induced by lipopolysaccharides as has earlier been shown for crayfish semigranular cells. The phagocytic capability of semigranular cells from crayfish was lost after exocytosis induced by the Ca2+ ionophore A23187, and under no conditions were the granular cells of crabs or crayfish seen to ingest bacteria in vitro. An opsonic function for the attaching proteins of a β1,3-glucan-activated haemocyte lysate was demonstrated using the phagocytic hyaline cells from crabs. Phenoloxidase appeared to lack opsonic properties.We suggest that, in crustaceans, opsonization takes place through hierarchically stimulated exocytotic release, and biochemical activation of the prophenoloxidase activating system: first from lipopolysaccharide-sensitive cells (semigranular cells of crayfish or granular cells of crabs) and then from granular cells, triggered by the initially released and activated prophenoloxidase system. Finally, “sticky” proteins of the activated prophenoloxidase system coat the invader, rendering it susceptible to the phagocytes (hyaline cells in both crab and crayfish and, to a lesser extent, semigranular cells of crayfish). These processes would, together, constitute a cellular communication pathway not previously demonstrated for invertebrates.

Exocytosis of the prophenoloxidase activating system from crayfish haemocytes

SummaryLipopolysaccharides (LPS) and the β-1,3-glucan laminarin G, both of which specifically activate the prophenoloxidase (proPO) activating system of crayfish haemocyte lysate, were found to induce degranulation (exocytosis) and subsequent lysis in vitro of monolayers of semigranular haemocytes from the crayfish,Pacifastacus leniusculus, (Table 1, Fig. 1 b), whereas the granular cells were unaffected (Fig. 1 c).Exocytosis of isolated semigranular or granular cells in vitro could also be evoked by the Ca2α ionophore A23187 (Table 2, Fig. 1 d). In this case, the whole proPO system was released from the cellular vesicles in its inactive form, since the secreted material contained protease and prophenoloxidase as inactive proenzymes, which could be activated if LPS or β-1,3-glucans were added (Table 3). The anion channel blocker SITS, which inhibits exocytosis in several systems, prevented degranulation triggered by β-1,3-glucan, LPS, or ionophore.It is concluded that, in arthropods, LPS serve as an indicator of Gram negative bacteria and β-1,3-glucan as an indicator of fungi. These non-self molecules elicit both the exocytotic release of the proPO system from the semigranular cells and the subsequent biochemical activation of this system.

Peroxinectin, a cell adhesive protein associated with the proPO system from the black tiger shrimp, Penaeus monodon☆

Upon activation of the prophenoloxidase activating system in the shrimp, Penaeus monodon, a cell adhesion activity in the haemolymph is generated. A cell adhesion assay showed that a high number of granular cells (60%) adhered to coverslips coated with a shrimp haemocyte lysate supernatant, whereas a very low number of cells adhered to coverslips coated with bovine serum albumin. Inhibition of adhesion by an antiserum against crayfish peroxinectin, a cell adhesion protein, revealed that the cell adhesion activity detected in shrimp haemocyte lysate supernatant might result from a peroxinectin-like molecule in shrimp. A cDNA clone encoding shrimp peroxinectin was isolated, which had an open reading frame of 2337 nucleotides, with a polyadenylation sequence and a poly A tail. It encodes a protein of 778 amino acids including a 20 amino acid signal peptide. The mature protein (758 amino acids) has a predicted molecular mass of 84.8kDa and an estimated pI of 9.0. Two putative integrin binding motifs, RGD (Arg-Gly-Asp) and KGD (Lys-Gly-Asp), were found in shrimp peroxinectin. Sequence comparison shows that the shrimp protein is similar to crayfish peroxinectin (69%) and to various peroxidases and putative peroxidases from invertebrates and vertebrates. The shrimp peroxinectin cDNA also shows similarity (51%) to both Drosophila peroxinectin-related protein (AAF78217) and peroxidasin (S46224), an extracellular matrix protein combining an active peroxidase domain as well as immunoglobulin domains, leucine rich repeats and procollagen-like motif. However, the sequence similarity to both Drosophila molecules are mostly within the peroxidase domain. Northern blot analysis, using a non-peroxidase region in peroxinectin as a probe, revealed that peroxinectin is constitutively expressed in shrimp haemocyte and was reduced significantly in shrimp injected with a beta-1,3-glucan, laminarin, to mimic an infection with a fungus.

Opsonic activity of cell adhesion proteins and β-1,3-glucan binding proteins from two crustaceans

A beta-1,3-glucan binding protein (beta GBP) from the shore crab Carcinus maenas was purified from plasma by precipitation of the protein at low ionic strength. The protein had a molecular mass of 110 kDa, and was shown to affinity precipitate with laminarin, a soluble beta-1,3-glucan, and to cross-react with an antiserum directed toward beta GBP from the crayfish Pacifastacus leniusculus. Also, a protein from the haemocytes of C. maenas with a molecular mass of 80 kDa was found to mediate cell attachment and cause degranulation of crab cells, similar to the 76 kDa protein present in the haemocytes of P. leniusculus. Antibodies against the crayfish 76-kDa protein reacted with the crab 80-kDa protein present in the granular cells. No 80-kDa protein could be found in the hyaline cells. Using a method with FITC-conjugated yeast particles in a phagocytosis assay, both the beta GBP and the 80-kDa protein from C. maenas were shown to have opsonic activity as had beta GBP and 76-kDa protein from P. leniusculus, resulting in higher levels of phagocytosis by the crab hyaline cells. Treatment of the yeast particles with beta GBP previously reacted with laminarin (beta GBP-L) only resulted in a minor increase of phagocytosis. Moreover, if the phagocytic cells were preincubated with beta GBP-L or with the 80-kDa protein, the enhancement of the phagocytic activity by beta GBP or the 80-kDa protein were abolished, indicating that a saturable number of one kind of cell surface receptor seem to be involved in phagocytosis.

Roles of integrin activation in eosinophil function and the eosinophilic inflammation of asthma

Eosinophilic inflammation is a characteristic feature of asthma. Integrins are highly versatile cellular receptors that regulate extravasation of eosinophils from the postcapillary segment of the bronchial circulation to the airway wall and airspace. Such movement into the asthmatic lung is described as a sequential, multistep paradigm, whereby integrins on circulating eosinophils become activated, eosinophils tether in flow and roll on bronchial endothelial cells, integrins on rolling eosinophils become further activated as a result of exposure to cytokines, eosinophils arrest firmly to adhesive ligands on activated endothelium, and eosinophils transmigrate to the airway in response to chemoattractants. Eosinophils express seven integrin heterodimeric adhesion molecules: α4β1 (CD49d/29), α6β1 (CD49f/29), αMβ2 (CD11b/18), αLβ2 (CD11a/18), αXβ2 (CD11c/18), αDβ2 (CD11d/18), and α4β7 (CD49d/β7). The role of these integrins in eosinophil recruitment has been elucidated by major advances in the understanding of integrin structure, integrin function, and modulators of integrins. Such findings have been facilitated by cellular experiments of eosinophils in vitro, studies of allergic asthma in humans and animal models in vivo, and crystal structures of integrins. Here, we elaborate on how integrins cooperate to mediate eosinophil movement to the asthmatic airway. Antagonists that target integrins represent potentially promising therapies in the treatment of asthma.

A CELL ADHESION FACTOR FROM CRAYFISH HAEMOCYTES HAS DEGRANULATING ACTIVITY TOWARDS CRAYFISH GRANULAR CELLS

A factor able to mediate cell adhesion of semigranular and granular haemocytes of the crayfish Pacifastacus leniusculus was recently purified from crayfish haemocyte lysate (Johansson and Soderhall, J. Cell Biol.106, 1795–1803, 1988). It is a protein with a mass of 76 kDa, and its activity seems to be generated concomitantly with the activation of the prophenoloxidase (proPO) activating system. In this paper, we present evidence that this same protein is also responsible for the previously reported degranulating activity of a crayfish haemocyte lysate, in which the proPO system has been activated. First, the 76 kDa band in SDS-polyacrylamide electrophoresis seems to be a single protein, since in isoelectric focusing the purified cell adhesion factor fraction migrated as one band with an isoelectric point of 7.2. Second, this fraction was also able to degranulate crayfish granular cells in vitro, and third, antibodies to this 76 kDa protein, which are known to block cell adhesion, could also inhibit degranulation in vitro.

The 76 kD cell-adhesion factor from crayfish haemocytes promotes encapsulation in vitro

SummarySemigranular cells from the crayfish, Pacifastacus leniusculus, were separated by Percoll gradient centrifugation and were used to study the encapsulation of foreign particles. The semigranular cells were found strongly to encapsulate glass beads coated with haemocyte lysate in which the prophenoloxidase-activating system had been activated with laminarin or with a low concentration of calcium ions. The granular cells only weakly encapsulated these particles. The encapsulationpromoting factor was purified from haemocyte lysates and found to be a 76 kD protein which was recognized by an antiserum to the previously described 76 kD cell-adhesion factor. After the last step in purification (Con A-Sepharose chromatography), the flowthrough consisted of several proteins, which had some, but less, encapsulation-promoting activity and contained a 30 kD band that was also recognized by the antiserum to the 76 kD cell-adhesion factor. If the haemocyte lysate prepared in low [Ca2+] was incubated with a β-1,3-glucan prior to purification, no 76 kD protein could be isolated but only a 30 kD protein. The 30 kD protein thus seems to be a degradation product of the 76 kD cell-adhesion factor. We conclude that the 76 kD protein which is released from degranulating haemocytes, and to a lesser extent its 30 kD fragment, can promote encapsulation. Phenoloxidase did not have any encapsulation-promoting activity.