Being an active part of a group or society (i.e., social integration) has been recognized as an important factor in promoting health and well-being in later life. With increasing attention on how social integration can lower morbidity and all-cause mortality in later life, recent studies point to immune response as a candidate link between social integration and physiological mechanisms. Given that physical aging is accompanied by elevated levels of systemic pro-inflammatory markers, such as interleukin-6 and C-reactive protein, social relationships emerge as a factor that can counteract aging processes associated with systemic inflammations. This chapter reviews how the increased inflammatory response (i.e., inflammageing) in late life may facilitate cognitive decline. Moreover, it focuses on how social integration or support plays protective roles in systemic inflammation functions. Finally, it reviews recent findings from health psychology regarding psychological factors, such as purpose in life and alteration of gut microbiome, that moderate the age-related risk factors for maladaptive immune function.