The use of mutants of Escherichia coli for the identification of human lymphocyte subpopulations in blood smears.

In previous work we have shown that some bacteria can bind to human lymphocytes and can be used to identify lymphocyte subpopulations in conventionally stained blood smears. These bacteria are of different species or genera, which makes it difficult to study the binding mechanism. Also, the main marker for B cells, Brucella melitensis, is of very small size and highly pathogenic. Here we show that B cells as well as some of the T cell subpopulations can be identified by different mutants obtained from a strain of an Escherichia coli. Two procedures were used to generate mutants. First, E. coli-YS57 (pro-his-trp-) was mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine and the binding to mouse spleen cells was used as a selective pressure. Second, phage-resistant mutants of E. coli-YS57 were obtained and tested for the ability to bind to lymphocytes. Out of 10 strains selected by the former procedure, 5 bound to a significant number of human lymphocytes. All four phage-resistant mutants bound to human lymphocytes. Out of the total of nine mutants that bound to lymphocytes, six bound consistently, i.e., they bound to similar percentages of peripheral blood lymphocytes from different normal donors. One phage-resistant mutant, E. coli USC-106, bound only to B cells. The subpopulations of lymphocytes identified by the mutants were essentially the same as those identified by different species or genera of bacteria. We concluded that E. coli mutants can be obtained that identify human lymphocyte subpopulations and that one of these mutants recognizes B cells; these mutants may be used to study the nature of the receptors for bacteria on lymphocytes, which appear to have a lectin-like nature.