C1q has long been studied and described for its central role in the activation of the complement classical pathway. This C1q molecule is able to recognize and interact with a large number of molecular patterns on pathogens or altered-self surfaces through its six C-terminal globular regions (GR). On the other side of the protein, the collagen-like regions (CLR) of C1q are generally associated with the soluble tetramer of C1r and C1s proteases (C1r2s2) that is responsible for the initiation of the complement cascade. Over the last years, several complement-independent functions were shown to be held by C1q through its interaction with various membrane receptors present on cell surfaces. Among these functions, the immune modulation properties of C1q have been recently described and were shown to engage immune receptors from the immunoglobulin-like (Ig-like) family: receptor for advanced glycation end-products (RAGE), CD33, leukocyte-associated Ig-like receptor 1 (LAIR-1) and LAIR-2. These receptors have opposite activities towards inflammation: RAGE triggers pro-inflammatory pathways whereas LAIR-1 and CD33 are immune inhibitory receptors. The C1q-mediated signaling differs whether C1q interacts with one or several of these receptors simultaneously. Recent studies suggest that RAGE and CD33 interact with C1q GR while LAIR-1 binds the C1q CLR, leading to a complex interaction network that congregates pro and anti-inflammatory signals, thus modulating the immune response. This PhD thesis aims at deciphering the fine details of C1q interaction with these receptors in order to provide fundamental insights into the C1q-mediated immune modulation. We mainly focused on the interaction of C1q with the collagen receptor LAIR-1. Thanks to the molecular dissection of C1q associated with competition assays and use of recombinant C1q variants, we showed that LAIR-1 binding site is located in close proximity to but is different from the one of C1r2s2 on C1q CLR. On the LAIR-1 side, we performed a mutational analysis based on literature and structural data to identify the key residues involved in C1q binding. These results led us to propose a model of C1q CLR interaction with the Ig-like domain of LAIR-1. Moreover, the specific recognition of C1q CLR by LAIR-1 led us to develop and generate the first recombinant production of C1q CLR (CLR_nc2). The replacement of the C1q GR by the second non-collagenous domain of collagen IX allowed the preservation of the specific C1q collagen chains registering. The CLR_nc2 was an important tool in the context of this PhD thesis and it will certainly also be useful for the future studies on C1q interaction with its many receptors.