SINDERMANN; INTERNAL DEFENSES OF CRUSTACEA 



fuses with the vacuolar membrane within the 

 phagocyte, releasing antimicrobial components 

 into the vacuole (Robineaux and Frederic, 1955; 

 Hirsch, 1965; Aarum, 1967). Evidence for 

 comparable intracellular events in invertebrates 

 is sparse, but Janoff and Hawrylko (1964) re- 

 ported lysosomal enzymes in clams and starfish, 

 and Eble (1966) found hydrolytic enzymes in 

 oyster phagocytes. 



Invading microorganisms are subjected to 

 antimocrobial factors both inside and outside the 

 jihagocytes. Substances of i)resumed cellular 

 origin, such as lysozynie, occur in the phagocytes 

 and the plasma. A great array of such antimi- 

 crobial factors was identified in vertebrates 

 (Skarnes and Watson, 1957; Elberg, 1960; 

 Hirsch and Cohn, 1960; Landy, 1960; Coombs, 

 Coombs, and Ingram, 1961; Mackaness, 1962; 

 Miles, 1962), and some counterparts were rec- 

 ognized in invertebrates. McDade and Tripp 

 (1967). for e.xample. reported lysozymes in oys- 

 ter hemolymph. 



In the vertebrates, specific and nonspecific 

 serum proteins increase the speed and effective- 

 ness of phagocytosis — the opsonizing efl^'ect 

 (Wright and Douglas, 1903; Suter, 1956; Row- 



Figure 2. — Role of cell membrane and lysosome break- 

 down in phagocytosis. 1-4; phagocytosis; 5-7: lysosome 

 activities. (Redrawn from Hirsch, 1965.) 



ley, 1960) . Sensitization of bacteria with serum 

 factors is not always a necessary prelude to 

 phagocytosis, however, as was pointed out by 

 Wood, Smith, and Watson (1916) and Wood 

 (1953). In the absence of other host responses, 

 early phagocyte activity may be important in 

 IH'eventing infection. 



Phagocytosis, then, constitutes the keystone 

 to resistance. As Aarum (1967) mentioned, 

 ". . . the organism's ability to opjjose infection 

 in-ecisely follows the phagocytes' ability to func- 

 tion oijtimally. Resistance is lowered by a low- 

 ering of phagocytic activity." Phagocytosis can 

 occur at the site of a lesion, in the filtering tissues 

 and organs of the circulatory system, and (to a 

 lesser extent) in the body fluid itself. Groups 

 of fixed phagocytic cells are present in many 

 crustaceans, most commonly in the sinuses and 

 lacunae of the gills and at the bases of the legs. 



Phagocytes agglutinate, aggregate, and co- 

 operate in defense — forming nodules (the "nod- 

 ules leucocytaires" of Cuenot, 1898), which are 

 also known in annelids, mollusks, echinoderms, 

 and other invertebrates. In a number of ani- 

 mals the nodules are bi'own, due to presence of 

 large numbers of brown granules in the phago- 

 cytes, which may be excretion products or de- 

 composition ]5roducts. In Gammaruti, the phago- 

 cytes composing the nodules secrete a clear 

 yellowish chitinoid substance around the para- 

 sites. This secretion gradually becomes dark 

 brown. The nodules ajipear as conspicuous 

 black spots in infected individuals (Pixell-Good- 

 rich, 1928) and are found frequently in gills and 

 appendages. It should be clearly understood, 

 however, that there are few detailed modern 

 studies of phagocytosis in crustaceans or other 

 invertebrates. Data from in vitro studies are 

 imrticularly scarce, so there should be no impli- 

 cation that the kinetics, energetics, or other as- 

 liects of i:>hagocytosis are fully understood. 



Hemocytes of crustaceans and other inverte- 

 brates also act in other ways to protect the in- 

 dividual from overwhelming microbial invasion. 

 Hemocytosis and hemocytic infiltration have 

 been described in a number of invertebrate 

 groups. Manifestations in invertebrates and 

 vei'tebrates involve proliferation of hemocytes, 

 changes in permeability of blood vessels, leakage 



461 



