(23)). HEK293T cells failed to localize to pericentromeric heterochromatin (PC-HC) and bind target DNA sequences. Co-expression of wildtype and mutant IKZF1 however, allows for IL-22BP localization to PC-HC and binding to DNA indicating a haploinsufficient mechanism of action for IKZF1L132P. Furthermore,Ikzf1+/L132Pmice have late onset defective immunoglobulin production, related to what is definitely observed in CVID individuals. RNAseq revealed a total loss ofHsf1manifestation in follicular B cells suggesting a possible practical link for the humoral immune response defects observed inIkzf1L132P/L132Pmice. == Intro == IKZF1, encoding for IKAROS, is definitely a zinc finger transcription element essential for immune cell development, homeostasis, and function (1). It was discovered to be of importance for both T and B cell development through the generation of an IKZF1 deficient mouse (Ikzf1/).Ikzf1/mice have a complete block of lymphocyte development in the fetal liver, resulting in the absence of mature B and NK cells, yet surprisingly, some T cells develop postnatally (2) but show problems in TCR signaling in the thymus (3). HomozygousIkzf1/mice are given birth to at the expected rate of recurrence and survive into adulthood (2). IKZF1 regulates transcriptional programs through the Lys05 coordination of six zinc finger (ZF) domains; the first four are essential for regulating gene transcription through DNA binding, and the last two help multimer formation as both a homodimer and as a heterodimer with IKZF1 and additional family members (4). IKZF1 is able to regulate gene manifestation through both activation (4-6) and repression of gene transcription (6-10). In B cells, once lineage commitment has been established, IKZF1 regulates B cell-specific genes that are important for further development and B cell function (6,11-16). Specifically, IKZF1 regulates Lys05 the BCR-signaling cascade during pro- to pre-B cell development (6,17,18), therefore ensuring correct progression through the early phases of commitment to the B cell lineage Lys05 and without which, B cells fail to develop. Additionally, germlineIKZF1mutations in cohorts of common variable immunodeficiency (CVID) individuals with low or absent B cells recognized a crucial part for right IKZF1 manifestation in maintaining normal B cell development and antibody production (19), as well as for self-tolerance of peripheral B cells (20) in humans. The specific mechanism of action for IKZF1 however, is not fully understood. In mice, the second and third zinc finger domains (ZF2 and ZF3) bind to core GGGAA motifs (5) in both traditional DNA sequences, as well as in satellite areas in pericentromeric heterochromatin (PC-HC), therefore facilitating chromatin redesigning and changes in gene transcription (6,7,9,21). In contrast, murine studies have shown that ZF1 and ZF4 are responsible for facilitating specificity by binding to flanking DNA sequences (22). Our understanding of IKZF1 biology has been greatly enhanced through the analysis of manyIkzf1mouse models (summarized in Heizmann, et al. (23)). A dominating negative mutation eliminating ZF1, ZF2, and ZF3 in the IKZF1 DNA binding website (Ikzf1DN/DN) Lys05 shows how IKZF1 is definitely important for hematopoietic stem cell commitment to the lymphoid lineage (24).Ikzf1DN/DNmice have a complete absence of all B and T cells and the majority die at a very young age due to increased opportunistic infections and septicemia (24). Mice heterozygous for this mutation (Ikzf1+/DN) show no obvious B cell problems, yet shed the manifestation of wildtype IKZF1 in the thymus and spontaneously develop T cell-derived leukemia and lymphoma (25). Recently, using CD23-CRE to conditionally delete IKZF1 in adult B cells, a conditional knock-out of IKZF1 was explained (Ikzf1B) (26).Ikzf1Bmice develop splenomegaly and autoimmunity due to the attenuation of anergy induction in follicular B cells (FoB) cells (26). A single point mutation in ZF3 (H191R,Ikzf1Plst/Plst) specifically disrupts the DNA binding ability of IKZF1 whilst still keeping protein scaffold structure and manifestation (27). This mutation however, is embryonically lethal, but analysis of the fetal liver shows a complete loss of B and T cell development (27). Originally, it was postulated the postnatal survival ofIkzf1/but notIkzf1Plst/Plstmice, was because of a market filling trait shared among Ikaros family members, that allows for payment for the loss of total protein expression (27). In the case.