Seven days of IgY treatment significantly suppressed virus shedding, duration of diarrhea, and disease severity when compared with untreated calves. these antitoxins because of their size and ease of management. Passive immunization was widely employed in EAI045 the 1920s and 1930s against human pathogens such asStreptococcus pneumoniae, Neisseria meningitides,andHaemophilus influenzae,in addition to tetanus and diphtheria. With the advent of cheaper and easier to use antimicrobials and antibiotics such as penicillin and streptomycin, it fell into disuse. Passive immunization only persisted for use in toxin-mediated diseases such as tetanus and botulism, virus diseases such as rabies, and in snake envenomation (Table 12.1). It is now staging a comeback. Polyclonal antibodies generated in immunized animals and monoclonal antibodies generated in the laboratory are EAI045 increasingly employed in the treatment of diverse animal and human diseases. == Fig. 12.1. == The principle of passive immunization. Thus serum from an immunized animal contains antibodies. When injected into another animal these can confer immediate, but temporary, immunity. == TABLE 12.1 . == Licensed Polyclonal Antibody Products for Animal Use in the United States == Immunoglobulins == The major antibody in mammalian serum is a protein called immunoglobulin (Ig)G. This is a Y-shaped protein of about 160 kDa. In passive immunization, whole or semipurified serum, or IgG obtained from an immune animal, is injected into or fed to another animal. If it is injected into an animal of the donor species then the injected antibodies will simply be removed through EAI045 normal catabolic processes. If IgG is injected into an animal of a different species it will act as a foreign antigen and trigger an immune response. EAI045 Such a response will result in its prompt elimination. It is therefore highly desirable to minimize the antigenicity of IgG. The simplest way of doing this is to treat the IgG with a protease such as papain or pepsin. These split the IgG molecule into two or three fragments. The first fragment to be cleaved off is the tail of the Y (Fig. 12.2). This fragment can be crystalized and so is called the Fc fragment. It does not contribute to toxin or virus neutralization so it can be discarded. The rest Rabbit Polyclonal to TAS2R12 of the IgG molecule consists of the two joined arms of the Y is called Fab2. This fragment retains the antibody activity. Further proteolytic digestion separates this into two antigen-binding fragments each called Fab. These too are functional. Elimination of the Fc region greatly reduces the antigenicity of the preparation although the smaller fragments do have a shorter half-life than intact IgG. == Fig. 12.2. == If immunoglobulins are injected into another species they act as antigens and are removed rapidly. If fragmented by treatment with proteases and unnecessary components such as the Fc region removed, this immunogenicity is minimized. As discussed later, modern molecular techniques also make it possible to alter the nonantigen-binding parts of immunoglobulins so that they too are identical to the recipient species and almost completely eliminating their antigenicity. == Polyclonal antibodies == A natural immune response to a complex EAI045 antigen such as a bacterium or virus activates large numbers of B cells that in turn generate a diverse mixture of antibodies, each with a different antigen-binding specificity. Most pathogens have a complex structure and present the immune system with many different epitopes. As a result, multiple B cell clones are stimulated to respond. These clones produce polyclonal antibodies. Polyclonal antibodies.