Research Question: How does the concentration of lipopolysaccharides from Escherichia coli O111:B4 treated to RAW 264.7 cells affect the degree of the cells’ in vitro morphological change? Thanks to Anton van Leeuwenhoek’s microscopic observations of cells, Louis Pasteur’s swan neck duct experiments, and many other microbiologists’ dedication, we are now aware that we live in a world teeming with microorganisms. Interestingly enough, we are worlds for the microorganisms ourselves; it is estimated that an average human body hosts approximately 100 trillion microbes, the number of which dwarfs that of human cells present tenfold. While some microorganisms, such as Lactobacillus acidophilus, are innocuous or even beneficial to their hosts, others, such as Escherichia coli O157:H7, can be pathogenic. Considering the staggering proportions in which microorganisms populate their hosts, the immune system—defensive mechanisms using the host’s biochemical substances to prevent infection--is essential for the latter’s survival. The innate immune system is divided into two contrasting subsystems: the innate immune system and the adaptive immune system. The innate immune system, on the one hand, occurs in all plants and animals and is activated immediately upon infection but cannot establish immunological memory; as a result, it can only provide non-specific responses against few pathogen-associated molecular patterns (PAMPs) that it was genetically encoded to recognize. The adaptive immune system, on the other hand, only occurs in vertebrates and requires the innate immune system to be activated but can establish immunological memory to provide highly specific responses against pathogens that it already encountered before. The innate imm... ... middle of paper ... ...phological change will be measured in the difference of average cell length and surface area compared to those of cells not exposed to LPS. Given the proinflammatory properties of TLR4 signaling pathway, it is hypothesized that both aforementioned differences will increase, suggesting a positive correlation with the concentration of LPS solution treated and the degree of morphological change in RAW 264.7 cells. By providing potentially corroborative evidence to widely studied yet insufficiently understood topic of immunology, this investigation hopes to offer greater insight into the underlying mechanisms of the innate immune system by analyzing their implications. The data from this research can also be applied to improve histological analysis of Gram-negative bacterial infection and to determine the effectiveness of future antibacterial or anti-inflammatory drugs.