Chapter 5 Parasite-Invertebrate Host Immune Interactions T.P. Yoshino! and G.R. Vasta 2 Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 125 2 How do Invertebrates Respond to Their Parasites? . . . . . . . . . . . . . . .. 126 2.1 Overview of Cellular and Humoral Immune Components . . . . . . . . . . .. 127 2.2 Protozoan Parasite Infections ............................ 129 2.2.1 Pathology and Cellular Responses. . . . . . . . . . . . . . . . . . . . . . . . .. 130 2.2.2 Humoral Responses .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 133 2.3 Parasitic Helminth Infections . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 135 2.3.1 Cellular Responses in Helminth Infections. . . . . . . . . . . . . . . . . . . .. 136 2.3.2 Humoral Responses .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 139 2.3.3 Killing Mechanisms ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 143 3 Evasion of Host Immune Responses . . . . . . . . . . . . . . . . . . . . . . . .. 144 3.1 General Mechanisms ................................. 145 3.2 Passive Mechanisms ofImmune Evasion. . . . . . . . . . . . . . . . . . . . .. 145 3.2.1 Intracellular Parasitism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 146 3.2.2 Molecular Mhnicry .................................. 147 3.2.3 Acquisition of Host Antigens (Molecular Masking) . . . . . . . . . . . . . . .. 149 3.3 Active Mechanisms of Immune Evasion. . . . . . . . . . . . . . . . . . . . .. 150 3.3.1 Destruction or Modification of Host Effector Cells . . . . . . . . . . . . . . .. 151 3.3.2 Immunosuppression and Immune Interference . . . . . . . . . . . . . . . . . .. 153 3.3.2.1 Immunosuppression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 153 3.3.2.2 Immune Interference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 154 4 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 156 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 158 1 Introduction Many of the preceding chapters and recent published reviews (Ratcliffe et al. 1985; Dunn 1986; Lackie 1988; Bayne 1990; Gupta 1991; Hultmark 1993; Ratcliffe 1993; Vasta et al. 1994) have amply documented the effectiveness and 1 Department of Pathobiological Science, University of Wisconsin School of Veterinary Medicine, 2015 Linden Drive West, Madison, Wisconsin 53706, USA 2 Center for Marine Biotechnology, University of Maryland Biotechnology Institute, UMS, 701 E Pratt St., Baltimore, Maryland 21202, USA Advances in Comparative and Environmental Physiology, Vol. 24 © Springer-Verlag Berlin Heidelberg 1996