The present invention relates to selectively controlling the function of a helper T cell. In the present invention, a mouse lacking a gene involved in ganglioside biosynthesis (ganglioside GM3 synthetase gene) (SAT-I KO) was produced and analyzed. As a result, the present invention provides, for example, a method for screening a substance which induces selective suppression of the function of a helper T cell in an immune response, including control of production of a sphingoglycolipid in the helper T cell, and moderation or suppression of an excessive immune response caused by the suppression of the function, that is, a substance having an immunosuppression activity, an anti-asthmatic action and/or an anti-allergic action.