Because splenectomy has been linked to overwhelming infection years ago, management of splenic traumatisms has become progressively conservative. To assess the immunological function of the spleen in patients with splenic traumatism of different intensity, 43 patients with splenic injury (grades I through V) undergoing either nonoperative management, splenectomy, splenectomy with autotransplantation, or splenic embolization were analyzed for lymphocyte subpopulations and antibody responses to Streptococcus pneumoniae and Haemophilus influenzae vaccinations. Patients treated with splenectomy exhibited a significant decrease in CD4+ T lymphocytes and in Immunoglobulin (Ig) M highIgDlow B cells (related to T-cell independent responses). Median fluorescence intensity of CD54+ in B cells also was reduced. The percent of IgMhighIgDlow B cells - a marker of marginal zone function - was inversely correlated with the number of pitted-red blood cells - a marker of red pulp function loss. IgM anti-S pneumoniae identified those patients with a defective rapid response to polysaccharide antigens. These results reinforce the importance of conservative options in the treatment of splenic traumatism for even a severely damaged organ. Despite the significant differences among the groups reported, it remains difficult to predict the IgM response to S pneumoniae vaccine of the individual patients. Better markers to assess splenic function and vaccination response after severe splenic traumatism - even in patients with nonoperative management - might improve risk assessment for overwhelming postsplenectomy infection. © 2011 Mosby, Inc. All rights reserved.