A lymphocyte activation inhibitor and a therapeutic agent for an autoimmune disease, each comprising, as an active ingredient, a sulfonamide derivative or sulfonic acid ester derivative represented by the following general formula (I):
wherein the ring A represents a monocyclic or bicyclic aromatic ring which may be substituted,
the ring B represents a 6-membered unsaturated hydrocarbon ring or a 6-membered unsaturated heterocyclic ring containing one nitrogen atom as a heteroatom, each of which may be substituted,
the ring C represents a 5-membered heterocyclic ring containing one or two nitrogen atoms, which may be substituted,
W represents a single bond or -CH=CH-,
X represents -N(R 1 )- or an oxygen atom,
Y represents a carbon atom or a nitrogen atom,
Z represents -N(R 2 )- or a nitrogen atom, and
R 1 and R 2 may be identical or different and each represents a hydrogen atom or a lower alkyl group, or a pharmacologically acceptable salt thereof, or a hydrate thereof.