In the TA3 murine mammary carcinoma system, the ability or inability of 4 sublines to grow in allogeneic mice is strongly correlated with the presence on the surface of a well characterized high molecular weight glycoprotein, GP-1. One of our new variants (Ha-variant) is of special interest because it arose from inoculated Ha cells by spontaneous metastasis and, unlike Ha, has the ability to grow subcutaneously while maintaining a high level of GP-1. We always find a strong positive correlation between in vivo shedding of GP-1 and the amount on the surface of TA3 tumor cells. We employ a highly sensitive (5ng) automated quantitative assay for GP-1 on the surface of intact cells (10 to the fourth power to 10 to the fifth power cells) or in serum (.05 ml) or other fluids. This hemagglutination-inhibition assay is based on the specific receptors of GP-1 for the lectin of Vicia graminea. We are also developing a radioimmunoassay for GP-1 and an indirect fluorescent assay for the detection of GP-1 tissue sections. We will study in syngeneic mice and the ability of the 4 sublines of TA3 to implant following tail vein injection and will attempt to select, by sequential passage of lung implants, for a line with the ability to metastasize spontaneously. We will correlate the ability of our sublines to implant or metastasize with their surface and serum GP-1 levels. We anticipate a strong positive correlation. The ability of purified GP-1 to promote metastasis will be studied. The potential immunosuppressive function of GP-1 will be examined in a number of systems, including the effect on syngeneic tumor specific immunity. We will also pursue preliminary indications that the GP-1 might be a carcinofetal protein and will determine the immunosuppressive potential of such a fetal glycoprotein analogue. Our automated assay will be used to screen several human lines for a wide variety of lectin and antibody receptors. This approach to glycoprotein detection and quantitation is of clinical interest because of its potential application to widespread screening.