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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.

In the rosette inhibition assay, thymopoietin was active and its activity was enhanced in the presence of high concentrations of ubiquitin. Facteur thymique serique (FTS) was active in the same assay, but its activity was completely inhibited by high concentrations of ubiquitin. Mixtures of thymopoietin and FTS showed activity both in the presence or absence of ubiquitin depending on the concentration of thymopoietin or FTS in the mixtures. There seemed to be an important biologic interaction of thymopoietin and FTS when presented as a mixture, suggesting that thymopoietin and FTS might interact in vitro and possibly in vivo .

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).

Serum thymic factor (facteur thymique serique, FTS) induces in vitro differentiation of T-cell precursors into more mature cells with T-cell characteristics. As isolated from porcine serum, FTS is the nonapeptide GIp-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn. We have described two radioimmunoassays that detect FTS but not other thymic hormones [Ohga et al., (1982) J. Immun. Methods, in press]. One assay is based on a monoclonal antibody from a hybridoma derived by fusion of mouse myeloma cells and spleen cells from a mouse immunized with an FTS-mouse IgG conjugate. The second assay is based on the antiserum from a rabbit immunized with FTS bound to F(ab')2 fragments of rabbit IgG. The detailed antigenic specificity of these anti-FTS antibodies was determined by measuring the ability of FTS and 12 synthetic FTS peptide analogues to compete with a radioiodinated FTS analogue in these radioimmunoassays. The mouse monoclonal antibody and the rabbit antiserum showed similar structural requirements for binding of the FTS peptides. Since FTS had been attached to the carrier proteins through the ϵ-amino group of Lys-3, both antibodies were relatively insensitive to omission of 1 or 2 N-terminal residues, replacement of Glp-1 with either Ala or Tyr-Ala, or substitution of Lys-3 with Ala. In contrast, binding of FTS to the antibodies was substantially decreased by omission of 3 or 4 N-terminal residues, omission of 2 or 3 C-terminal residues, or replacement of Gly-7 or Asn-9 with Ala. Relative to the mouse monoclonal antibody, the rabbit antiserum was more sensitive to the omission of 4 N-terminal residues and much more sensitive to replacement of Gln-5, Gly-6, or Asn-9 by Ala. Both antibodies were relatively specific for molecules ending in -Xxx-Xxx-Gly-Gly-Ser-Asn-OH, which corresponds to the biologically active region of FTS.

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.

The effect of zinc deficiency (Zn − ) on the circulating thymic hormone (FTS) levels in A/J mice was studied. After 3 weeks of feeding the mice a Zn − diet, FTS levels were markedly reduced and after 17 weeks, FTS was undetectable. By contrast, the zinc-supplemented (Zn + ) group seemed to maintain FTS levels better than the normal diet group with aging. On the other hand, spleen spontaneous rosette-forming cells (sRFC) were studied for their azathioprine (AZ) sensitivity in A/J mice on different diets. The Zn − mice had fewer sRFC than did the normally fed or Zn + mice. The role of zinc in controlling levels of FTS and thus thymic function is discussed.