Final answer:
In hematology, a left shift indicates an increase in immature neutrophils, also known as 'bands' or band cells, which are an early response to infection.
Step-by-step explanation:
A left shift is a term used in hematology that refers to the presence of increased numbers of immature neutrophils, specifically ones where the nucleus has not fully segmented and appears like a band, known as "bands" or band cells. These immature neutrophils are also called granulocytes that stain with a neutral dye and are an indication of an active response to infection. Neutrophils are the first responders to infection, are phagocytic, and are crucial for the innate immune response. Regarding their development, neutrophils arise from myeloid stem cells in the red bone marrow and as they age, their nucleus becomes more lobed, leading to the mature forms referred to as "polys".