The hypothesis of this study is that the hypogammaglobulinemia from the immune dysfunction and the induction of NF-kB from the inflammatory process are, in part, responsible for the development of pneumonia and other infectious complications identified after TBI. This study has two specific aims: The primary specific aim of this study is to determine the association between serum immunoglobulin or NF-kB levels and the development of pneumonia in patients suffering from traumatic brain injury (TBI). The secondary specific aim of this study is to determine the relative contribution of clinical variables such as APACHE II-III Score and Injury Severity Score as compared to immunological variables (serum immunoglobulins and NF-kB) to the development of pneumonia in patients suffering from TBI.