FIRST BOSTON <FBC> SWISS AFFILIATE BOOSTS STAKE First Boston, the Swiss affiliate of First Boston Inc, said it raised its stake in the company to 11,262,307 shares, or 35.5 pct of the total, from 10,262,307 shares, or 32.8 pct. In a filing with the Securities and Exchange Commission, Financiere Credit Suisse said it bought 870,100 First Boston common shares between Feb 10 and 27 at prices ranging from 48.125 to 53.000 dlrs a share, or 22.5 mln dlrs total. It said it bought the shares as part of an agreement to raise its minority stake in First Boston to 40 pct, the same stake level First Boston holds in Financiere Credit Suisse.