The antigenic constituents of sporulated Cryptosporidium parvum oocyst antigens were characterized with antisera from mice immunized against C. parvum. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining defined the major proteins. Six of seven lectins used recognized as many as 15 bands. The lectins concanavalin A, Dolichos biflorus, and wheat germ agglutinin showed strong activity against the same eight bands with molecular weights ranging from 72,000 to greater than 100,000. An enzyme-linked immunosorbent assay was used to detect antibody to C. parvum. Antibody binding was significantly decreased by heat and enzymatic treatment with trypsin, protease, and mixed glycosidases. C. parvum antigens were further defined by the reactivity of immune sera with a C. parvum sonicate preparation separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretically transferred to nitrocellulose paper. Antisera from orally infected mice consistently recognized four antigens with molecular weights ranging from 72,000 to greater than 100,000. These antigens also bound concanavalin A. Treatment of the antigen preparation with mixed glycosidases reduced the reactivity of antisera with most antigens with molecular weights greater than 60,000. The data suggest that the antigenic composition of C. parvum is complex and that carbohydrates alone or in association with lipids or proteins may be important in the immune response to C. parvum.

Pre-T cells that differentiate in the thymus into mature T cells are believed to arise in the bone marrow, although the circulating form of the putative T cell precursor has not been identified (1, 2). The defining characteristic of a mature T cell is the expression of an antigen-binding receptor (TCR), which is characteristically (ifnot universally) associated with CD3 proteins . The majority ofT cells in peripheral blood express the cdo form of the TCR (TCR2), and a minority (1-3%) express they/S chains (TCR-1) (3). These receptors are encoded by genes that rearrange in T cell precursors, with y chain rearrangement commonly occurring first. Although CD3 and the TCR are known to be acquired in the thymus, the possibility of extrathymic differentiation has not been excluded .One of the earliest T lineage antigens, CD7 (gp40), is expressed before TCR-ß gene rearrangement and surface expression of CD1, CD2, and CD3 antigens and persists on most mature circulating T cells (4-6). CD7 has been demonstrated within the bone marrow (1) and on fetal lymphocytes before colonization of the thymus (4, 7). Depletion of CD7+ cells from bone marrow results in the loss of T cell colony-forming capacity (2,8). Cells that are CD7+CD3 -(typically CD16+) are known to exist in peripheral blood and display natural killer activity (9).These studies were designed to test the hypothesis that the circulating form of the T cell precursor has a surface phenotype of CD7+CD3-, and could be induced to differentiate into CD3 + cells outside the thymus . We found that CD7 +CD3 -cells purified and cloned from normal human peripheral blood by FRCS differentiate into CD3 + cells in the presence of IL-2, PHA, and irradiated feeder cells. These CD3+ cells include cells that are TCR1+ or TCR2+ and express various combinations of other T cell surface antigens .