64 D. A. L. DAVIES 



inert material for comparison with the active products of other 

 tumours. The material was indeed inactive in H-2-K and also 

 H-2-D^EK systems, but other specificities have not been tested. 

 The ability of this tumour to grow in all kinds of mice in the 

 face of H-2 incompatibility is of some interest. Mice can be 

 immunized against this tumour, e.g. BALB/c mice immunized 

 with BP8/C3H remain susceptible to CL2 but are resistent to 

 LAN. 



The necessity of using fresh (i.e. not freeze-dried) material for 

 extraction and all activity studies is a great inconvenience but in 

 spite of the lability of the material, suspensions, after sterilization, 

 have been kept for many months without detectable loss of 

 activity. 



The information obtained so far is in substantial agreement with 

 the views recently expressed by Herzenberg and Herzenberg 

 (1961) that H-2 activity might be associated with lipoprotein 

 derived from the membrane fraction of cells, but the product 

 isolated from ascitic fluid has not shown any indication of 

 structure when examined in the electron microscope. 



Summary 



(i) Mouse H-2 antigens have been extracted from the products 

 of ascites tumours, and an increase in activity of at least 500-fold 

 was obtained by a simple fractionation procedure. 



(2) Activity has been measured by inhibition of the haemagglu- 

 tination induced with mouse anti-mouse sera by the dextran- 

 normal human serum technique. 



(3) The product is a lipoprotein; information about its homo- 

 geneity has been difficult to obtain but evidence for impurities 

 has been sought but not found. The proportions of lipid and 

 protein vary between 30 and 50 per cent lipid with 70 and 50 

 per cent protein, 



(4) The protein component has species specificity and is part 



