Methods for modulating immune responses are provided. The methods involve contacting an immune cell with an agent that modulates interaction of a compound comprising a Lewis antigen with the immune cell such that production by the immune cell of at least one cytokine that regulates development of a T helper type 1 or T helper type 2 response is modulated. In one embodiment, the agent is a stimulatory form of a compound comprising a Lewis antigen, such as a Lewisy, Lewisx or Lewisa oligosaccharide, or a derivative thereof. In another embodiment, the agent is an inhibitory form of a compound comprising a Lewis antigen, such as a Lewisy, Lewisx or Lewisa oligosaccharide, or a derivative thereof. In various embodiments, the immune cell is a human immune cell, a macrophage or a T cell. Pharmaceutical compositions for modulating immune responses are also provided.