The influence of immunization with (T,G)-A--L on the frequency and characteristics of [(125)I] (T,G)-A--L-binding cells (ABC) was investigated in high and low responder mice, whose ability to respond to (T,G)-A--L is under control of an H-2-linked immune response gene, Ir-1. Unimmunized high and low responder mice have about the same number of ABC in spleen and lymph nodes (6-12 ABC/10(4)). However, after immunization with (T,G)-A--L in aqueous solution, ABC in high responders increase to a much greater extent than they do in low responders. By inhibition of ABC with class-specific anti-Ig sera, it was demonstrated that in nonimmune and primed mice antigen is bound to IgM receptors, which is in agreement with the exclusive production of 19S anti-(T,G)-A--L antibody in primed animals. In contrast, after secondary challenge with antigen, ABC in high and low responder mice have mainly IgG receptors, although under the conditions used for immunization, low responders are not able to produce detectable amounts of 7S anti-(T,G)-A--L antibody. From these results and from the evidence that low responders very probably have a T cell defect, it is suggested that the switchover from IgM to IgG precursor cells can be induced by antigen itself, without the action of specific T cells. Furthermore, the failure of marked proliferation of ABC in low responders after antigenic stimulation is explained by the lack of stimulation by specific T cells. By independent methods it has been shown that all ABC detected in this study are B cells. Preliminary experiments indicate that purified peripheral T cells bind antigen, but much less per cell than do B cells.

Animals↗

PubMed1973

In vitro assembly of bacteriophage Lambda heads.

The assembly of plaque-forming particles in cell-free extracts of induced lambda lysogens was observed two ways. (i) DNA isolated from a lambda-related phage, 434 for example, is added to an extract of an induced lambda lysogen, and plaque-formers with the genotype of the added DNA are detected. (ii) One extract from an induced lambda lysogen that carries an amber mutation in one of the head genes (A, B, C, D, or E) is mixed with one carrying an amber mutation in a different head gene; an increase in the number of lambda plaque-formers is found over that in either extract alone. These plaque-forming particles have the properties of normal phage particles. They are resistant to DNase, although DNase added to an extract before addition of DNA prevents their appearance; they have a sensitivity to neutralizing antibody and a specificity of adsorption to bacteria characteristic of the source of the extract, but they have the genotype of the added DNA; and they have about the same bouyant density as phage particles. Mutants in genes B, C, or D can donate DNA to the phage formed by complementation between extracts of different mutants, but mutants in genes A or E cannot. Complementation occurs between a pair of extracts only if one (or both) is a DNA donor. This observation suggests a tentative pathway for head assembly: that the products of genes A and E act before those of B, C, and D.

Centrifugation, Density Gradient↗

PubMed1973