Immunity and Resistance 649 



Adhesion tests 



Adhesion, or "adhesin," tests, in diagnosis of trypanosomiasis, in- 

 volve mixing citrated blood from the host with a suspension of the 

 suspected parasites. A positive test, in which red corpuscles and some- 

 times blood platelets stick to the flagellates, indicates that the blood con- 

 tains antibodies specific for the trypanosomes. The reaction apparently 

 depends upon the presence of complement (195). Adhesion tests have 

 been applied to diagnosis of trypanosomiasis in man and other animals 

 (37, 66, 132, 179, 195) as well as infections with Leishmania tropica (116). 



SEROLOGICAL DIFFERENTIATION 

 OF SPECIES 



In the differentiation of species by means of serological reactions, 

 microorganisms are tested with known antisera. A positive reaction, such 

 as agglutination, indicates that the antiserum contains antibodies homol- 

 ogous for the test organism. This establishes the identity of the strain, 

 provided group reactions have been eliminated. The specificity of an 

 agglutin test can be increased by preliminary absorption of the anti- 

 serum with appropriate heterologous antigens so as to eliminate some or 

 most of the group antibodies. Even the quantitative interpretation of 

 group reactions may throw some light on degrees of taxonomic relation- 

 ship (85, 186). Serological tests have some value in differentiating morpho- 

 logically similar organisms, but the data must be interpreted cautiously 

 because the tests are so sensitive. For instance, agglutinin tests have 

 distinguished between strains of trypanosomes derived from one original 

 stock but maintained in different host species (138). 



Agglutinin tests have given good results in differentiating types of 

 Leishmania. Bandi (11), who was interested in the status of "Leishmania 

 canis," found that either L. canis or L. donovani agglutinin would react 

 with either strain in titres up to 160. Neither agglutinin was active 

 against L. tropica in titres above 70. L. canis and L. donovani thus 

 seemed to be serologically identical, while both were distinct from 

 L. tropica. More recently, agglutinin tests have indicated that L. dono- 

 vani, L. tropica, and L. brasiliensis are serologically distinct (74, 97, 125), 

 although group reactions may be expected with low dilutions of aggluti- 

 nating sera. Group agglutination is eliminated in higher dilutions, while 

 homologous agglutination may still be detectable at titres of 2,560-2,580 

 (157). Adler and Theodor (1) used agglutinin tests in identifying an 

 invertebrate host of L. tropica with their demonstration that "Herpeto- 

 monas papatasii," an intestinal flagellate of sandflies, is serologically 

 identical with L. tropica. 



Specific lysins also have been tried in the identification of Trypano- 

 somidae. By inoculating flagellates into culture media to which known 



