HERBERT FISCHER Max-Planck-Institut fur Immunbiologie, Freiburg-Zahringen With 3 Figures Ladies and Gentlemen: On behalf of the organizers of the 22nd Mosbach Colloquium, Msrs. HOLZL-WALLACH, STOFFEL, WIEGANDT and myself, I bid you all a hearty welcome. We thank you all for coming and naturally feel particular appreciation for the presence of the invited speakers. But, thanks to the tradition that the Mosbach Colloquia have enjoyed for 22 years we did not need to work very hard, since most of our invitations were accepted without hesitation. Perhaps some of you will wonder why Mosbach and its...