Junctional diversity is essential to antibody activity.

Many mechanisms of antibody diversification have been shown to exist, including combinatorial pairings of heavy and light chains, the use of multiple gene segments (combinatorial diversity), and the imprecise joining of these gene segments (junctional diversity). The contributions of each of these mechanisms to functional antibody activity has not been fully explored, especially in the case of junctional diversity. A chain recombination experiment between an anti-arsonate monoclonal antibody and an anti-oxazolone molecule in which light chains differ essentially only at the V/J junctional position show that junctional diversity may play an important role in antigen binding.

Use of JH4 joining segment gene by an anti-arsonate antibody that bears the major A-strain cross-reactive idiotype but displays diminished antigen binding.

One of the antibody families utilized by the A/J mouse in its response to p-azophenylarsonate (Ars) is characterized by the expression of the major anti-arsonate cross-reactive idiotype (CRI) of the A strain. This family has been termed the Ars-A family. A hybridoma antibody (HP 101F11 ) obtained after immunization of an A/J mouse with Ars was identified initially as displaying the CRI, but was subsequently found to bind antigen at a level much lower than most members of the Ars-A family. The results of binding studies suggested that HP 101F11 possesses reduced avidity for antigen. When isolated light and heavy chains were allowed to recombine with the heavy and light chains of a strongly antigen-binding, strongly CRI-positive antibody of the Ars-A family (HP 93G7 ), the low level of antigen binding by HP 101F11 was found to be due to a structurally variant heavy chain. Whereas antibodies of the Ars-A family with normal avidity for antigen had been shown to use the JH2 joining segment gene, amino acid sequence analysis of HP 101F11 revealed that this antibody has a JH segment with a sequence identical to that encoded by a portion of a different JH gene, JH4 . The implication that 101F11 uses the JH4 gene instead of JH2 was supported by the observation that the productively rearranged gene is associated with an Eco R1 restriction fragment 0.95 Kb smaller than the corresponding fragments of Ars-A hybridomas with normal avidity for antigen. The size difference of 0.95 Kb corresponds exactly to the known distance between the JH2 and JH4 genes in BALB/c germline DNA. In addition to the structural differences immediately attributable to the use of JH4 , HP 101F11 has shown an amino acid interchange in the DH segment, and a single amino acid deletion at the DH-JH boundary. These results show that variation among members of the Ars-A family in the DH and/or JH segments provides alternative structural forms of Ars-A antibodies upon which selective processes can operate during the course of an immune response.

Regulation of rates of cholesterol synthesis in vivo in the liver and carcass of the rat measured using [3H]water.

This study was undertaken to determine the mechanisms that regulate cholesterol synthesis in vivo and to quantitate the relative importance of the liver and extrahepatic tissues as sites for sterol synthesis. Rats were administered [3H]water intravenously and killed 1 hour later. The amount of [3H]water incorporated into digitonin-precipitable sterols was then measured in liver, whole blood, and the remaining tissues of the carcass. In control animals, killed at the mid-dark point of the light cycle, rates of [3H]water incorporation into sterols equaled 2290 and 103 nmol/hr per g, respectively, in the liver and carcass. Cholesterol feeding suppressed synthesis in the liver but not in the extrahepatic tissues, while fasting for 48 hr suppressed synthesis in both the liver and carcass. In fasted animals subjected to stress there was a 5-fold increase in hepatic synthesis but no change in synthesis by the extrahepatic tissues. Similarly, incorporation of [3H]water into sterols by the carcass was unaffected by light cycling while the liver showed a definite diurnal rhythm. In control rats, 34.5 mumol of [3H]water was incorporated into sterols by the whole animal per hour. Of this amount of sterol synthesis about 54% took place in the liver while the remaining amount occurred in the tissues of the carcass. With cholesterol feeding or fasting, or during the mid-light phase of the light cycle, synthesis in the extrahepatic tissues accounted for 69 to 90% of total body sterol synthesis.