Other studies about the CTL response against extracellular pathogen were carried out by Meissner et al. that demonstrated a vigorous CD8+ T cell influx into the lung in response to Pneumocystis, an extracellular fungal pathogen [34], and by Mehrzad et al. (2008) that showed that trafficking of CD8+ T cells during initiation of Escherichia coli mastitis is accelerated when increasing the E. coli inoculum dose [35]. The gene discussed is CD8A; the disease is mastitis.