A major obstacle in understanding the signaling events that follow CD28 receptor ligation arises from the fact that CD28 acts as a costimulus to TCR engagement , making it difficult to assess the relative contribution of CD28 signals as distinct from those of the TCR .
a major obstacle in understanding the signaling events that follow cd28 receptor ligation arises from the fact that cd28 acts as a costimulus to tcr engagement , making it difficult to assess the relative contribution of cd28 signals as distinct from those of the tcr .
O O O O O O B-other_name I-other_name O O B-protein_molecule O O O O O O O B-protein_molecule O O O O O B-protein_family_or_group O O O O O O O O O O O B-protein_molecule O O O O O O O B-protein_family_or_group O