Then another... or two other assays became available that were done in vitro and you transfer the whole interaction between immune cells into a tissue culture. One was the so-called mixed lymphocyte reaction where you... as the name says, you mixed donor and recipient... well, lymphocytes of two strains actually that differ in the H2 complex and if you kept them in culture for a while then the lymphocytes began to proliferate... divide and you can count the number of... the increase in the number of cells and thus measure the histocompatability. Again, it had to be modified because originally both cells... they were both lymphocytes though one reacted against the other and the other reacted against the first so you got... you could not distinguish which direction the reaction was going.  But eventually the one cell was irradiated so it could not... or chemically inactivated... so it could not react and then it became a one-way mixed lymphocyte reaction. That was the second assay.  And the third was actually an expansion of the mixed lymphocyte reaction where people realized that the cells, after they have divided, some of the cells become killer cells. That means if you then use them on a target... particular target cells, then they would kill these cells and methods were developed how you can count the killed cells.

So there were these three assays and we began... we were interested whether any of these, or whether there is a difference between the K D on the one hand and the IA antigens on the other in any of these assays so that would tell us something whether they are like the K and D, the classical H2 antigens, or whether they are different... something very different. Of course other people were... it was very hard at that time to come up with anything that somebody else wouldn't have the same idea and would not be doing it, others were doing many of the same things, and so there was again very strong competition.  But not only that, there was also controversy. Different people were finding different results... somewhat different results. In our tests we could find some difference, but between K D and IA... but it seemed like it was merely a quantitative difference that both types of antigens were able to mount the response but it was... there was some difference in the quantity of the reaction. Other people claimed that there was principle difference. That means the claim was in the end... I'm simplifying quite a bit now... in the end the claim was that K and D will not stimulate mixed lymphocyte reaction and graft versus host reaction but will... sorry, yes, right, sorry. So once again, K and D will not stimulate the mixed lymphocyte reaction graft versus host reaction and IA will very strongly. In contrast, K and D are good targets of CML, or the cell mediated cytotoxicity, while the IA doesn't give any cytotoxicity, and that was very strongly and widely spread opinion of many people.