Macrophage content of spontaneous metastases at different stages of growth.

The macrophage content of spontaneous metastases has been quantified morphometrically for a panel of rodent tumors at different stages of metastatic tumor growth. Using a histochemical technique to selectively stain macrophages, we have evaluated the relative content of macrophages in spontaneous pulmonary metastases from the 13762NF MTLn3 rat mammary adenocarcinoma and the B16-BL6 mouse melanoma, as well as in spontaneous hepatic metastases from the M5076 mouse reticulum cell sarcoma and from autochthonous reticulum cell sarcomas in SJL/J mice. Between 112 and 254 separate, individual metastases were evaluated for each of these tumors. The data show that the relative macrophage content of very small metastases is high. However, as metastases grow the relative macrophage content falls, reaching uniformly low levels by the time the metastases are 0.5 mm in diameter. These data are very similar to our previous observations on experimental metastases where the same pattern of high macrophage content in small metastases was seen. Finding the same pattern in more slowly growing, spontaneous metastases of tumors derived from several different tissues and in two species suggests that the fall in relative macrophage content is not a phenomenon isolated to experimental metastases, a particular site, or a tissue of origin for the tumor. The relative decrease in macrophage content may thus be a general phenomenon with important implications for immunotherapy directed to enhancing the tumoricidal activity of macrophages.

Changes in the macrophage content of lung metastases at different stages in tumor growth.

The macrophage content of experimental B16 melanoma metastases at different stages of their growth has been quantified with the use of morphometry in conjunction with a recently developed histochemical method for selectively staining intratumoral macrophages. Data are presented from analyses of 954 sections of 155 individual lung metastases, showing that the macrophage content of individual B16 melanoma lung metastases not only varies significantly but also falls dramatically once metastases contain more than 700 tumor cells. In addition to providing new information on host response reactions of micrometastases, these experiments also indicate that conclusions on intratumoral macrophages derived from studies of large primary tumors and metastases in advanced stages of growth may have little or no relevance to events in micrometastases.

New histochemical method for measuring intratumoral macrophages and macrophage recruitment into experimental metastases.

A new double-label histochemical method is described which permits accurate quantitation of macrophage recruitment into neoplastic lesions in situ. Intratumoral macrophages are identified by their capacity to ingest colloidal iron particles from the interstitial fluid. Since colloidal iron is retained in a stable form within these cells for a considerable time, new macrophages that emigrate into the tissue after injection of the colloidal iron are identified by their ability to ingest a second colloid (lanthanum) which can be reliably distinguished from the initial iron label. Preexisting (colloidal iron label) and newly recruited macrophages (lanthanum label) are identified in serial sections by histochemical methods using hydrogen peroxide oxidation to detect iron (blue reaction product) and cleavage of phosphate esters to demonstrate lanthanum (magenta reaction product). The macrophage content and macrophage recruitment were found to vary substantially in individual metastases within the same host.

The effects of hypobaric atmospheres on living cells in layers of thin media and implications for electron microscopy.

At present, the only possibility for improved resolution of intracellular movement appears to be electron microscopy using a hydration chamber (EMC) at reduced gas pressures with thinned medium around the cells. The environmental constraints of examining cells under such conditions were examined in the absence of ionizing radiation by using an EMC-analogue fitted to a light microscope. White blood cells and baby hamster kidney cells were examined. A 50% survival pressure value, for hypobaric atmospheres, was determined for these cells. Morphological changes of the hypobarically-exposed cells are described.