Fill in the Blank in the Following Paragraph Regarding the Innate

Fill in the blank in the following paragraph regarding the innate and adaptive immune systems. Do not use abbreviations.
"As key components of the innate immune response, … cells provide the link between the innate and adaptive immune responses. Upon exposure to pathogens in tissues, they engulf the microbe, become activated, and travel to nearby lymphoid organs where they present the processed antigens to the lymphocytes of the adaptive immune system."