Changes in the Marrow Reserve of Eosinophils Following Re‐exposure to Foreign Protein

In an earlier investigation (Hudson, 1960), the quantitative methods developed in this laboratory (Yoffey, 1960) were used to demonstrate the magnitude of the ‘reserve’of mature and nearly mature eosinophils in normal bone marrow. The question arose as to the circumstances under which this reserve might be drawn upon. Numerous investigations have shown that eosinophil granulocytes have an important role in the response to foreign protein and that increased numbers are found in blood and bone marrow following repeated exposure to the same antigen (e.g. Schlecht, 1910; Speirs, 1960; Litt, 1960; Winqvist, 1960). It has also been noted by several investigators (Hajós, 1928; Biggart, 1932; Samter, 1949) that at a definite interval after re‐exposing a sensitized animal to a foreign protein, there is a very striking circulatory eosinophilia which, the observations of Homma (1921) suggest, may be accompanied by a temporary decrease in the percentage of eosinophils in the bone marrow. However, the possibility that there may be a depletion of the marrow reserve of eosinophils in these circumstances has not hitherto been investigated by quantitative methods. It seemed important, therefore, to study these methods to study the blood and bone‐marrow eosinophils of the guinea‐pig during the phase of marked circulatory eosinophilia which follows the reinjection of foreign protein.