The local inflammatory responses following intraperitoneal injections of various antigens were studied using quantitative methods of determining the cells of the blood and peritoneal fluid. The following observations were made in a study of over 200 adrenalectomized mice:

1. The number of blood cells was found to average higher and to be significantly more variable than had been previously observed in normal mice. There was a temporary neutrophilia following the injection of the non-specific as well as specific antigen. Injections of a pollen extract into pollen-sensitized mice produced an eosinophilia 4 to 7 days after injection, which corresponded with a local accumulation of these cells at the site of antigen injection (peritoneal cavity). This did not occur when the non-specific antigen (bovine albumin) was injected. The blood lymphocytes and monocytes on the other hand did not appear to reflect the local accumulation of mononuclear cells at the site of injection.

2. There were very marked qualitative and quantitative cellular changes in the peritoneal fluid following an injection of antigen. These changes depended upon the antigen injected, the degree of sensitization of the animal, and the presence or absence of the adrenal gland.

a) The neutrophils appear in the peritoneal fluid within one hour following the injection of either albumin or pollen, and disappear almost entirely by the 2nd day. At 4 and 12 hours after injection the number of neutrophils was found to be significantly greater in adrenalectomized mice. There was no significant difference in the degree of neutrophilia between the specific and non-specific responses to albumin. However, pollen produced a greater neutrophila in pollensensitized mice, than it did in albumin-sensitized mice.

b) There was also a difference in the manner in which the mononuclear cells reacted to different antigens. Within 48 hours, bovine serum albumin produced an increase of 170 per cent in the cells of animals not previously sensitized to albumin, and 230 per cent in albumin-sensitized mice. Pollen on the other hand, produced no significant change in the mononuclear cells of animals not previously sensitized to pollen, but an increase of 220 per cent in animals previously sensitized to pollen. This response occurred 10 days after the reinjection of pollen.

c) Adrenalectomy produced a decrease in the average number of mast cells found in the peritoneal fluid. No significant changes were observed in the number of these cells following injections of specific or non-specific antigen.

d) The eosinophil responses in the peritoneal fluid were found to be of two types. There was an initial non-specific accumulations of these cells which disappeared by the 4th day. This occurred only in adrenalectomized mice. When pollen or albumin was injected into either adrenalectomized or normal animals which had been previously sensitized to that antigen, a pronounced and prolonged eosinophilia occurred lasting up to 10 days. This response was found following repeated injection of a number of different-antigens, and it appeared to be a specific response of the sensitized animal. The number and proportion of eosinophils was found to be consistently higher in the adrenalectomized animals.

In conclusion, it was noted that the local cellular responses to an antigen depended upon (a) the nature of the antigen injected, (b) the state of sensitivity of the animal injected, and (c) the presence or absence of the adrenal gland. A local accumulation of eosinophils between the 2nd and 10th days after the injection of a non-toxic antigen appeared to be the specific cellular response of the sensitized animal. Therefore, the eosinophil must be considered along with the plasma cell, lymphocyte and reticulo-endothelial cell as a possible source of antibodies.

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