Antigen-binding Cells

Since B lymphocytes have receptors on their surface, they can selectively bind antigen. Bound antigen can be visualized by means of radioautographic techniques, rosette formation, enzymatic reactions and fluorescent techniques. In this section, I intend to collect some estimates on the frequency of antigenbinding cells from normal non-immunized animals. Because the estimation of the frequencies by these techniques is not based on analyzing the capacity of cells to produce an antibody response, special attention must be paid to the specificity of the binding and its relevance to the antibody response. 

None of the above experiments demonstrated whether the binding is achieved by B or T cells. Dwyer et al. (1971) performed antigen binding experiments using nude mice, and results similar to those with normal mice were obtained. 

The specificity of binding (Naor and Sulitzeanu, 1967) was demonstrated by inhibition of binding with an excess of non-iodinated BSA. While a 1000-fold excess of BSA inhibited the binding of iodinated BSA, a 100000-fold excess of HSA did not. 

Bach et al. (1971) DECREusEFONDetal. (1970) Greaves and Hogg (1971) Haskill and Axelrad 

In Table 3 are given the frequencies of antigen-binding spleen cells from non-immunized mice as measured by several authors. It is evident that the 

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Aminoalkylsilane atomic absorption spectroscopy Amino acid transporter alpha-1-antitrypsin Adenoassociated vims Abscisic acid, a plant hormone ATP-binding cassette antigen-binding cell... 

In conclusion, the frequencies of antigen-binding cells reported in this section can be considered as upper limits for precursor estimates. The number of cells physiologically significant as precursor cells in a given antibody response is unknown. 

The antigen-binding method is not based on analyzing the capacity of cells to produce antibody. It is not known what fraction of antigen-binding cells is capable of giving an antibody response. Thus, the frequency of antigen-... 

Julius, M. H., Masuda, T., Herzenberg, L. A. Demonstration that antigen-binding cells are precursors of antibody producing cells after purification with a fluorescence-activated cell sorter. Proc. nat. Acad. Sci. (Wash.) 69, 1934-1938 (1972). 

Unanue, E. R. Antigen binding cells. II. Effect of highly radioactive antigen on the immunologic function of bone marrow cells. J. Immunol. 107, 1663-1665 (1971)-... 

Figure 15.19 Schematic representation of the peptide-binding domain of a class I MHC protein. The al and a2 domains are viewed from the top of the molecule, showing the empty antigen-binding site as well as the surface that is contacted by a T-cell receptor. (Adapted from P.J. Bjdrkman et al.. Nature 329 506-512, 1987.)...

T-cell receptors (TCR) are heterodimeric transmembrane glycoproteins found exclusively in T cells, with extracellular domains that closely resemble antibody Fab structures. Each of the TCR a and p chains forms half of an extracellular antigen-binding domain, and in addition has one transmembrane... 

Part of these T-lymphocytes transform into memory cells. These cells are different from their ancestors in that they are activated by a much lower antigen binding strength and also much less depend on signal 2. Now self-antigens can activate these T-lymphocytes. As during activation continuously new memory cells are formed, autoreactivity is sustained and autoimmune disease follows (Fig. 2). 

Class IIHLA molecules are expressed on the surface of antigen-presenting cells. They play a key role in presentation of processed linear peptide antigens of at least nine amino acids to T cells. Antigen is bound to the HLA antigen binding cleft formed by the a and 3 chains of the HLA class II molecule. This tri-molecular HLA-antigen complex binds in turn to the variable portion of the T-cell receptor. 

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