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Thymic function was evaluated by quantitation of circulating thymic factor in patients with several forms of severe infantile immunodeficiency diseases. Direct quantitation of thymic factor in serum of patients with severe combined immunodeficiency revealed heterogeneity of this syndrome by this parameter, as was also shown by study of susceptibility of the marrow cells to differentiation in vitro. Thymic factor was not detectable in one patient with severe combined immunodeficiency, but was present in normal or near-normal concentrations in three others. Circulating levels of this hormonal activity were also not detectable in a patient with DiGeorge athymic syndrome. Following marrow or fetal liver transplantation, which corrected the severe combined immunodeficiency thymic factor levels either increased slightly or did not change appreciably. Fetal thymic transplantation, which together with fetal liver transplantation corrected the immunodeficiency in one patient with severe combined immunodeficiency, was associated with increase of thymic factor to normal levels. Fetal thymus transplantation alone, which was employed to correct the immunodeficiency of DiGeorge athymic syndrome, caused an increase in thymic factor activity to normal or near normal levels in this patient.

Thymic secretory function was assessed by determining levels of circulating thymulin-like activity in plasma of 21 pediatric patients infected with the HTLV-III/LAV retrovirus. All the patients had serum antibodies against p41 antigens of HTLV-III on Western blot analyses. In accordance with the latest definition established by the Centers for Disease Control, 14 patients had the acquired immunodeficiency syndrome (AIDS) and the remaining 7 were classified as having AIDS-related complex. Their ages ranged from 1 to 7 years, with 10 being less than 1 year of age. Circulating thymulin activity, normally highest in healthy children under 15 years of age, was undetectable in 11 patients and below normal range for age in the remaining. OKT4/OKT8 ratios of T-cell subsets in peripheral blood were below normal in the majority of patients. Our findings suggest that thymic epithelial injury may be an early event in HTLV-III/LAV-related disease and may precede the development of clinical and/or immunologic aberrations.

Levels of Facteur Thymique Serique (FTS) were measured by rosette inhibition assay in the sera of patients with mycosis fungoides (MF) and Sezary syndrome (SS). Increased levels of FTS were detected in 15 of 23 patients with MF. Two patients with SS showed normal values. The biological activity quantitated in the serum was shown by specific immunoabsorption using anti-FTS antibodies to be due to FTS and not to allogeneic factors (AF).

Summary Markers for T lymphocytes and in vitro differentiation of PBL and marrow cells under the influence of human thymic extract were studied in a patient with ataxia telangiectasia. Certain populations of cells from blood and marrow could be differentiated in normal controls and in our patient by human thymic extract to develop characteristic markers for T lymphocytes.

The effect of thymus extract on the development of cell surface antigenicity in two patients with primary immunodeficiency was studied and compared. A stem cell fraction from bone marrow preparations of a patient with severe combined immunodeficiency failed to develop cells with antigenic markers of T-lymphocytes while that of a patient with common variable form of immunodeficiency who had both severe functional deficits of T-lymphocytes and agammaglobulinemia developed cells with such markers after treatment with thymus extract. These findings indicate that the two forms of severe combined immunodeficiency disease studied have different bases which may be reflected in differences of response to differentiative influence of thymus extract.

A new radioimmunoassay (RIA) is described for the quantitation of thymosin alpha-1 (alpha-1). The assay employs an antiserum specific for the COOH-terminal half segment 15-28 of alpha-1, synthetic alpha-1-(15-28) as the hormone standard, and a radioiodinated N alpha-acetyltryrosyl-alpha-1-(15-28) as the tracer. Since alpha-1-(1-28) lacks a phenolic ring for direct radioiodination, the N alpha-acetyltyrosyl-alpha-1-(15-28) was synthesized by the solid-phase method. The peptide bears a Tyr in place of Lys in position 14 of the natural peptide. It showed full alpha-1-(15-28) immunoreactivity and its radioiodinated derivative served as tracer in the RIA. An anti-alpha-1-(15-28) antiserum was raised in a rabbit and was shown to recognize alpha-1-(15-28) or its tyrosyl analogue, and the peptide, alpha-1-(1-28). But it did not recognize other thymic hormones or the biologically active segment 32-36 of thymopoietin, or structurally unrelated peptides. It could also detect natural alpha-1 cross-reacting material in the cytoplasm of cultured human thymic epithelial cells as measured by indirect immunofluorescence. In the RIA, as little as 9 pg of alpha-1-(15-28) equivalents in a 50 microliter sample could be detected. In addition, alpha-1-(1-28)-like immunoreactivity was quantitated in 6 human thymus homogenates and ranged from 0.5 to 4.5 ng/mg of protein.

Recently it has been found that children with severe combined immunodeficiency (SCID), who are thought to lack lymphoid stem cells capable of developing into either the B- or T-lymphocyte populations, do not possess cells in their marrow which can be induced by partially purified thymic extracts to differentiate into T-lymphocytes in vitro . The initial observations were made with marrow cells from three untreated infants with SCID under the same conditions which revealed clear evidence of induced differentiation in normal individuals. Marrow cells and peripheral blood lymphocytes from two of these children were studied again after bone marrow transplantation (BMT). Clear indication of precursor cells was obtained in marrow and blood after successful transplantation. The newly acquired precursors could be differentiated in vitro into T-lymphocytes under the influence of thymic extracts. T-cell characteristics were established both with a specific anti-human T-cell serum (ATCS) and by the E-rosette technique using sheep red blood cells (SRBC). This approach reveals a new means of dissecting the immunodeficiency diseases before BMT and a method for assessing cellular reconstitution after marrow transplantation.

Zinc deficient humans and animals have depressed thymic mass and increased susceptibility to infection. In the present studies, we investigated the relationship between cellular immunity, thymic hormones, and serum zinc levels in 19 patients with common varied immunodeficiency. Five (26%) had serum zinc levels 2 SD below normal and 11 (58%) had abnormally low lymphocyte proliferation to at least one mitogen. A significant statistical correlation between zinc levels and lymphocyte proliferation to phytohemagglutinin and concanavalin A was identified. Forty-two percent had abnormally low levels of facteur thymique serique and 74% had low levels of thymopoietin, although no statistical relationship between the levels of these hormones, zinc levels, or lymphocyte proliferation could be identified. Three patients with the most profound zinc deficiency had substantial increases in thymic hormones after zinc repletion, and two had complete resolution of intractable diarrhea. A therapeutic potential of zinc for certain patients with hypogammaglobulinemia is suggested.

Four radioimmunoassays (RIA) are described for the quantitation of serum thymic factor (facteur thymique serique, FTS), a thymic peptide hormone. Each assay employs an antibody specific for FTS, synthetic FTS (Glp-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn) as the hormone standard, and a radioiodinated FTS analogue as the tracer. Since FTS lacks a tyrosine residue, 2 FTS analogues were synthesized by the solid-phase method with tyrosyl-alanyl or 3-(2,6-dichlorobenzyl)tyrosyl-alanyl in place of the amino-terminal pyroglutamyl residue (Glp). They showed full FTS immunoreactivity and their radioiodinated derivatives served as FTS tracers. Two assays used the antiserum from a rabbit immunized with an FTS-protein conjugate. Two other assays used a monoclonal antibody against FTS produced by a hybridoma derived from mouse myeloma cells and splenocytes from a BALB/c mouse immunized with an FTS-mouse IgG conjugate (Ohga et al., 1982). All 4 RIAs were specific for FTS. The more sensitive rabbit antiserum can detect as little as 1 pg of FTS in a 50 microliters sample, which may allow quantitation of the FTS circulating in human peripheral blood.

Transplantation of two fetal thymuses failed to reconstitute the immune function in a patient with the DiGeorge syndrome. Serum thymic hormones (facteur thymique serique and thymopoietin), which had been nondetectable, became normal after thymus transplantation. Studies done on the patient's fractionated bone marrow cells in vitro appeared to reflect defective capacity for T-lymphocyte differentiation. In spite of the efforts at treatment, the child died at 2 years of age, apparently due to an associated cardiovascular abnormality. At autopsy, no thymic tissue could be found. Failure of immunologic reconstitution after fetal thymus transplantation in this patient with the DiGeorge syndrome may have resulted from deficiencies of precursor cells.